The way you worded it made it sound like you were talking about consumer memory.
Edit: Samsung, Hynix, Micron et all. DO have memory running at 2133mhz, just not at density's needed (1G) to achieve a 16x16bit layout with 16Gb.
Microsoft could achieve it with a 32x16bit layout, but that would just be stupid.
Edit 2: Regardless, I think we put the RAM rumor to rest at any rate. :P
--::{PC Gaming Master Race}::--