I have quite a large collection of Japanese HID lamps which I bought from Japan. Many of them are mogul base.

I've noticed that the 200w and 250w lamps use either a bt28, ed28 or bt32 outer envelope. However, those envelopes have a neck that is longer than a standard bt28 or ed28 lamp.

I think the reason for this is they will fit better in fixtures designed for 400w bt37/ed37 lamps without adjusting the optics. Another reason could be the short neck bt28 or ed28 lamp would not fit because the neck is too short.

This seems to apply for many of their fixtures like floodlights or streetlights.

I have found documentation of fixtures listing wattages of 110-400w HID: Floodlight, Pole Light, Cobrahead

The 110w refers to an HPS or CMH lamp with a mogul base and a bt28 long neck envelope.

As far as I know, I haven't seen long neck bt28 or ed28 HID lamps used anywhere else other than Japan.

I was under the impression that the long neck envelopes for the 200W and 250W Japanese lamps was to ensure that the arc tubes would align with the optics of Japanese fixtures designed for higher wattage lamps.

I think this shape is great for having less waste in production and high quality rates. In production the outer glasses rotates very fast and with the top glass pipe they're probably better to hold in position. By common E-shape lamps you often see inclined glued glas on sockets. Never seen that on a BT lamp.
And you can make that "pipe" easily longer. For replacing lamps like you wrote ;-)