Good point, it's not in v6M, though it is in v8M baseline, which is the v8 equivalent. So M0, M0+ and M1 don't have it but I think everything else M-profile should.
Given that Ken said most ARM processors, the nerd sniping becomes: what percentage of all ARM cores are M0/M0+/M1. I'd guess a lot (maybe not half though). Don't all micro SD cards have a processor inside them? They're probably almost all ARM...
