Also, Safari is a little bit different than Mail and iChat, in that it is based on open source-code... Apple probably feels a need to update Safari more frequently to keep up with all the other open source geeks.
Safari is as of yet a beta, and not a fully released program like Mail or iChat. As such, it will probably be released in June at the WWDC with Panther, and if Apple hasn't updated everything else by then, they need to get medication for OCD.