They may be using an off-the-shelf x86 core, but their actual CPU die may have all kinds of customizations on it (like the addition of a GDDR5 memory controller). AIUI GDDR5 memory is much more expensive than DDR3. So it may happen eventually, but I don't think it will be any time soon, and believe me, I really want PCs to be better than consoles in every way.
It just seems to me that whatever they're doing with AMD, AMD is going to be able to farm out to other parties. Given that both MS and Sony are using AMD cores paired with GDDR5 memory controllers, it seems almost certain that there's nothing approaching an exclusivity contract to prevent AMD from now selling that bundle to any maker of gaming PCs or SteamBox builds or whatever else.
And the current/historical cost differential between DDR and GDDR5 certainly seemed to be a considerable problem back when these specs were first rumored. But the following things suggest that's not likely to be an issue preventing it from hitting other gaming PCs:
1. Sony managed to spec 8GB of it into a box they simply can't afford to subsidize greatly at the outset. [1]
2. Sony and MS both need to know the cost of any expensive components will drop massively over the next couple years.
3. PC gamers readily and regularly accept higher prices for their machines than console makers could ever stomach.
So I don't see it becoming common. Truly very few non-gamers would care about the performance delta. But it seems like a thing that will be on offer from multiple vendors, for feasible prices, before long. (Particularly given that AMD could really use any edge against Intel.)
[1] People wrote off a lot of the rumors on that basis alone. If Sony is confident that it can not only afford GDDR5 for system memory, but that it can afford so much, there has to be a massive price cut incoming.
