Actually the X360 vs PS3 is not unlike the comparison of PS1 and Saturn, performance wise. PS3 has theoretically more cpu grunt but it is very hard to max it out and it is arguable if it really is more powerful or not for pure math - just like the Saturn with its double SH2 + DSP.
But both the PS3 and Saturn were significantly outclassed in GPU power, and it took for so long for games to have efficient enough code to close the distance.
I still say the major reason why PS3 caught up graphics wise isn't because the Cell is so magically powerful, but because Microsoft abandoned everything to pursue the Kinect which was a dead end.