> AGP variants require a bridge chip, and that hasn't worked well with the R500 card.
> So, it isn't an artificial restriction, supporting AGP variants requires extra work.

I'm not sure how to conclude the requirement of extra work just from the fact that the faster AGP transfers don't work with the AGP variants. So yes, their bandwidth is lower than it could be, but where does the extra work come from for supporting the AGP variants?