Why do most (if not all) miners use a form of Fermat's primality test (http://en.wikipedia.org/wiki/Fermat_primality_test), instead of another probabilistic test?

Sure, it's fast, but wouldn't something like the Miller–Rabin test (http://en.wikipedia.org/wiki/Miller-Rabin_primality_test) work a bit better (according to the Wikipedia article, the big-O time is the same.