I'm not sure why this is so poorly supported across design apps - even Photoshop (at least on the versions I own) doesn't have it and the only straightforward game in town seems to be Fireworks.
These days, most of my exported files for web site themes are 8 Bit PNG with alpha transparency. it just makes sense.
And it's quite a wrench to the workflow to have to jump out of AD just to make these conversions and manual optimisations in another app. There is quite an efficiency hot as it's not just a matter of running a conversion script, each file has to be individually reoptimized from 24 bit with transparency down to 8 bit, selecting the colours etc
Please could this one be a priority?
T