Doesn't need to be, it just needs to play games. Looking at the PS3 first-party titles & Naughty Dog, they don't appear to be struggling with the hardware, in fact, it just appears to be getting better and better as time goes on.
http://www.youtube.com/watch?v=Az0CXkyoWjgAs for "more powerful than a PC", considering when it came out, they still hold their own, even if the hardware world has moved on. I've upgraded my PC twice since buying my PS3, yet besides Crysis and S.T.A.L.K.E.R. they're playing the same games.
There are certain things that the Cell excels at - floating point calculations being the main one. However, it needs the software to be written for it, it doesn't just work with any old program. The i7 is a general purpose CPU - a jack of all trades, but it doesn't really excel at anything in particular.
