x58-i820 lol ... more likely x69
but put that aside, intel and amd are not the whole computer world.
rambus done an excellent job with xdr, in fact so good that micron and others used their ideas in ddr2/3..4 chips. (and federal curt looks favorably in this kind of industrial espionage i wonder what ati would say 2-3 from now about their secrets gone to envidia by that stanford runaway dally)
and after all as small memory market player they targeting consumer electronics where lower cost and smaller number of modules make a big difference. in fact it wouldn't be too much of surprise that tegra2 use xdr interface instead ddr2. it's simply more power efficient and as it came out more bang for buck when small size matters.