A PC with 4GB DDR3 and 2GB GDDR5 is enough to run modern games at 1080p with no RAM bottlenecks. I guess something to do with the unified architecture and single memory clock, but it seems like a very expensive solution.
Anyway, I'm pretty happy with the PS4 reveal overall, mainly because they confirmed you can keep it offline if you want to. The games will come in time, early adopters will get burned/bored as usual. Nothing new for a big console launch.