Based on this page: http://www.corsair.com/products/dominator/default.aspx
the A model supports Intel Extreme Memory Profiles (XMP).
After double checking the New Egg listings, I see that it does state A supports XMP and B supports BEMP (Black Edition Memory Profile).
If your're comfortable setting timings by hand I don't know why it would matter. However I'm not familiar with BEMP. Here's one explanation I found: http://www.hardwarezone.com.au/reviews/view.php?cid=2&id=2880&pg=2
Googling around, there are others who bought the "wrong" RAM, such as this one: http://www.overclock.net/intel-memory/638214-bought-wrong-ram-bemp-instead-xmp.html
Another indicates AMD hasn't actually enabled the BEMP for these modules yet (as of 12/09) http://www.overclock.net/amd-memory/621613-corsair-dominator-cmd4gx3m2b1600c8-amd-bemp.html
Neither seemed to have a problem getting it running though.