The UPR cat'ed X-pipe I was running on my Notch was listed as being for 5-speed cars "only"; however, it bolted up to Frankenstang's '86 GT with AOD without any problems at all, so I dunno. I couldn't see anywhere that having a T-5 versus an AOD would make those things fit any differently. Most X- and H-pipes use the same location for their tranny crossmember hangers (if they have hangers at all), and the AOD didn't seem to be significantly wide enough to cause any problems as far as I could see with fitment.
Maybe just something they put on there to cover their butts, even though it was kind of a pointless gesture...?
Most of the manufacturers like BBK, UPR and such make xpipes that will work for both AOD and 5 speeds. It cuts down on their material and development cost since they just have to make one pipe. There are a few that are 5 speed only. I know that Dr Gas made an X that was 5 speed only and their might be a few others.
Kinda like LT headers. You are quite limited on LTs for an AOD car.