Actually the AIW 8500 128MB is more closely related, sharing the same feature set other than the GPU and amount of memory. The 8500dv differs a little in that it uses a tuner on silicon rather than the phillips analog tuner the AIW 7500 and AIW 8500 use, also the 8500dv uses a VIVO breakout box that includes both input and outputs, while the AIW7500 and AIW 8500 use seperate Breakout box for video input, and a multi-gang Video-output adapter.
Also, the 8500 cards support ATI's DVI>Component-out dongle while the 7500 does not.
As far as analog video capture, and multimedia features, you can consider them all to be equal.