wouldnt a 128 bit OS need a 128 bit processor? not 100% sure, but I dont think that there are many desktop processors that have 128 bit instruction sets yet. May be there with the LGA2011 in SB and bulldozer, but probably not.
They usually go up in powers of two. x86 started as 16-bit with the 8086, then 32, then 64.even then, shouldnt they go to 96 instead of 128? (32+32 to get 64, 64+32=96?)