As a note for online stuff: Virtua Fighter 5 (dethroning VF4 as best fighting game ever) on PS3 will support VF.Net that is used in arcades. I tinkered around with it when I went to Japan (I still have my access card, hope it works on PS3) and it's pretty freakin' awesome. VF4's was similar I'm sure, but that's a few years old already.
I'm not sure if it will have head-to-head fighting online (the arcade one doesn't as far as I've seen), but there is a *lot* of other stuff you can do. I didn't explore much of Tekken 5's online stuff, but even VF4's online stuff (a game that's a few years older) was more extensive. VF5 blows it away completely.

DOA4 has been doing online pretty well since it came out. Lag is uncommon, but it handles it in an interesting way. The entire game slows down so that both sides are seeing the same thing at the same time. It's definitely weird, but better than missing a counter or reversal because of lag.

Online for any 3D fighter can work if they can figure out a way to deal with lag. Latency will be a problem in any online game for a long time, so unless they are waiting for everyone to have 1gb/s transfer speeds to have real online fighters, they have to work around it.