hmmmm well see, there is a rather high yield with micron ddr3, no doubt, the problem is many mfgs see that as a reason not to bin at all.
they try to save costs by just selling all sticks as 1800 or 1866 without ever testing them and rmaing the few ones that fail than putting up the effort of properly binning them.

and another reason is binnind ddr3 isnt the same as binning ddr2, so some that bin dont do it right which results memory not running at rated speeds