Most spread videocard vram is 1024 MB and there's not any significantly better gpu in the top 10 gpu steam stats compare to what's in Orbis (1st is even an Intel HD 3000..). That's the PC gaming right now, not some limited editions of 500$ gpu with double amount of memory.
Sony's choice of GDDR5 will certainly fuel some evolution for the standard. 8gb chips by 2015-2016 seems likely now.
IMO PC gaming isn't defined by what the average gamer uses, it's defined by what's available to every gamer. The games will just be console ports with enhanced image quality options regardless so there's little argument to be made about how average hardware power effects PC game development.
The fact is that if you're a PC gamer and you want more power, you buy it (if you want it enough of course). If you're a console gamer and you want more power your only option is to become a PC gamer. That's why we focus on the high end systems when making comparisons. Because those high end systems are open to anyone that wants to spend the money on them. Looking at lower end systems is obviously relevant as well since the barriers to entry are lower at those price points but looking at what people are already using makes no sense to me. Those PC gamers all have the option of moving to more powerful hardware and if they choose not to then that means they are likely already satfisied with the hardware they have, in which case, why should that concern us? It obviously doesn't concern them.
Or to put it another way, as a gamer if I want a system that will play all next generation games at 1080p/60fps in full 3D, of what relevance to me is the fact that 99.9% of all the other gaming systems out there (console or PC) are unable to achieve this? My only concern is whether such as system exists and if so, what is that system. If it's a console, then I can look to console gaming, if it's a PC, I need to look to PC gaming.