Maybe in 2010 GHC will start working on Snow Leopard. Fingers crossed.
GHC doesn't have an awful lot of people working on it, certainly compared to something like GCC. There is no maintainer for x86_64 on OS X; essentially, those of us without the skill to resolve the issues are just hoping that someone steps up.
This Trac ticket has more details; you can see from the length of the CC list how much interest there is in resolving this. Unfortunately, interest doesn't directly translate into a fix.
SBCL is in the same position. I can (and did) compile/install it manually - but that doesn't change the fact that it's "broken."