http://lists.gnupg.org/pipermail/gnupg-ru/2004-December/000158.html
Given the extent of the discovered weakness and the likelyhood that people won't be installing this release more than a few years down the road, this seems to me to be an overreaction. Ah, well. Hopefully it is known that SHA1 is truely more secure than MD5, rather than just that there have been no alarming reports yet.
Since Fedora is supposed to be bleeding edge and the place to try new technologies, this lets this mechanism get tested by those willing to take the risk, before it gets deployed to the more conservative products.
