Re: the 64 bit address space is "huge"
You build 128-bit applications not because of the address space but because of the increase in bus speed throughput. With a 128 bit bus you load twice as much data to the CPU in one cycle as well as increasing the speed at which the CPU processes the data..
Now, you can argue we've already passed the point at which loading data to the CPU and/or SPU processing speed has a meaningful effect to the average punter. I hold that opinion myself. But I recognize the theoretical advantage of the higher bus throughput as well as the fact that there exists a market for which that increase is useful.