After seeing that almost every 2 lamp F40T12 preheat fluorescent autotransformer ballasts for the North American market are high power factor ballasts, I am beginning to wonder if any low power factor 2 lamp F40T12 preheat fluorescent autotransformer ballasts were marketed in North America as well.

I've think that the multiple amount of HPF ballasts in the US market, is because high power factor is much more important in the US and Canada markets than in 220-240V markets. I've recently discovered that US electrical devices consume much more current than the electrical devices of 220-240V countries to maintain the same wattage rating, which means that a US HPF ballast, would consume much more current than a simple 230V series choke without a PFC capacitor at all to maintain the same wattage rating.

The F40 ballast for a 120V mains need a transformer functionality. If the fixture would be designed as NPF full power ballast, at least the primary of that transformer would have to be able to handle almost 200VA because of the high reactive power. By making it a HPF design, the primary has to handle just the real power, so about 120VA or so. And that difference means quite a cost saving on the transformer part, so the cost of the extra capacitors required for HPF get offset by a cheaper transformer design, so the overall cost to produce either of them is about the same. And when you have the same cost, there is not much motivation for paying for stronger wiring (in larger commercial installations) related to NPF. So making the NPF makes not much sense.

Now a bit different story are the residential ballasts. At first these tend to be more often just a single lamp units. There the thermal budget has to be able to handle both present, as well as missing lamp. With a HPF ballast the missing lamp would mean higher primary loading, so its design would have to count for that, so would have to be "beefier" than just the 60W for a full power ballast.
Second most residential fixtures are in fact designed to drive the lamp at reduced power levels (residential use often called for less harsh, less bright light). That means all powers scale down. In that power territory the ballast component cost become dictated not that much by the amount of material used, but it is dominated by its complexity. So having 100VA winding gets cheaper than a 60VA winding plus an extra capacitor.
And on top of that the residential fixtures tend to be used way less than  commercial, so they spend way more time off and have to last way longer in terms of years from the day of manufacture. There the paper capacitor technologies have big drawback: When not in use, they tend to draw in humidity and fail even when running very little hours. Avoiding the capacitors makes them way more resilient in this way, so able to really last the running hours lifetime even when spread over decades.

In 230V Europe the NPF vs HPF means the HPF has just a capacitor extra, no savings on any material, so there is quite significant manufacturing cost saving potential by just not using the PF correction in the fixtures. But that was prevented by the minimum standard imposed on the fluorescent fixtures (in force since 70's energy crisis; requiring the ballasts to meet efficiency minimum, so banning all resistive ballasts, ballasts not capable of driving the tubes so they do not reach their designated light outputs and imposing minimum requirement for power factor).

Medved, do our (mostly 120V mains) transformer-ballasts for fluorescent lamps have a functional inductor after transformer secondary?  If we were to consider a single lamp, three wire, ballast: does it contain basically just a transformer primary and secondary, or is there an additional inductor after transformer secondary?

Zou won§t find the inductor there as a dedicated component, but it is integrated along the voltage conversion function into one high leakage transformer. It is verz common to do these integrations, as sepaerate device would need separate winding and that would be another loss contributor.

A couple years ago I assumed/imagined, transformer ballasts (rapid start or preheat) contain a choke/inductor.  Perhaps as a discrete component; or perhaps another section of winding, after transformer secondary, manufactured together with transformer in one assembly/component.  Recently I wondered: whether that is necessary, or whether transformer secondary has enough inherent inductance to obviate/preclude a further inductive stage/winding.  Thank you Medved, for confirming my suspicion.

edit 2022-02-05: Here, I assumed too trigger start ballasts use a choke aside from transformer.

To make a transformer and inductor in one (aka high leak tarnsformer) you form a path for magnetic flux between the primary and secondary. So the simplest core shape would not be like "O" (so a single magnetic circuit), it would be more like "8". There the magnetic flux from the primary can split into part flowing through the secondary coil and part flowing directly back. The second path, called a magnetic shunt, has then an air gap in its way, so there is some reluctance (aka magnetic resistance) in the path for that branch of the flux. This reluctance is, what then dictates the series inductance "visible" on the secondary.

So you need specially designed core shape for these integrated components. But because it saves a lot of power. Redirecting magnetic flux via complex paths is almost lossless, but converting the magnetic flux/tension back to electric voltage/current by winding is where majority of the losses are. The only drawback is, you need custom shaped core plates, so it means higher tooling costs to set up the production and because these shapes do not align that well on the raw sheet material (lke e.g. EI shapes does) for cutting from the raw sheet material, you end up with a bit extra more wasted material. But you save on the copper cost and then your customer during operation on the power losses.

The HX transformers are the simplest form of integrated nmagnetic components, a bit more complex are the cores for CWA ballasts (there the magnetic shunt has to exhibit predefined saturation curve), more complex are the cores for mag reg ballasts requiring two shunts and three winding sections (one primary winding, shunt, resonance winding, shunt, secondary winding), other are the magnetic regulator stabilizers, tradditional magnetic amplifiers, and even complete power electromagnetic passive pack for modern high density resonant DCDC converters (there the thing integrates even the resonance capacitors within the winding assembly; of course, there the magnetic circuit is made of ferrite because we are talking about 200kHz+ operation).

In this case, are HX autotransformer ballasts simply autotransformers with an integrated choke?

From the functionality perspective, yes, that is exactly what they are. A transformer with a choke within one unit.