Yea, processors have hovered at 32 and 64 bit for a while. Some processors have what you call a VPU or vector processing unit which runs at 128bit. Really, there is not much advantage of going to 256 or 512 bit processing because that only allows larger numbers to be processed/moved. In the future there may be need for larger vector units to address more memory, but currently 64bit processors can addres 16gigs of memory. That is a lot of memory.....
BTW, to say the dreamcast or any other machine is 128 bit is really misleading. To my knowledge there has never been a mainstream 128 bit CPU and only parts of current CPUs are 128bit.
