UPDATE:
Sorry to resurrect an old thread, but it seems (and I'm probably not the only one to have noticed this) that SeatCounter is now actually showing AP inventory. D and W classes, for purely AC flights, are showing (and, from my experience, fairly accurate).
What's interesting to note is that, searching for some random dates in the far off future, one never sees more than 2 seats in D on one flight. Finally a confirmation on this? So much for 10% of the cabin...
On that note, it would also appear I inventory is no longer showing up on SeatCounter. I've tried the availability.publicbackup.com, tandt.com, and
www.geocities.com/farebuckets sites...all don't show I, either. Does that leave KVS as the only remaining source?