For SLI you need two exact PCI-E models and this little bridge chip that connects the top of them both to communicate.
I don't know where you're seeing people comparing SLI to one card, the only time I see it is in benches which isn't to say like "haha nvidia wins" but simply to show where each card stands.
Besides ATI will be coming out with their own form of SLI
Updated G70 info....says PS3 will be around 550MHz core, so we can assume that the G70 will probably be around there as well, quite different from the 430 speculated in the previous specs in this thread, not only that, but 90nm architecture as well compared to 110nm listed in here.
Soooo basically god knows what this thing will actually be lol