Unfortunately for anyone hoping to completely maul a PS3 owner via Unreal Tournament 3, cross platform play between the PC and the PS3 will not be available at launch. According to an Epic representative, "The biggest challenge in doing cross-platform play is synchronizing the builds such that the build on the PC is 100% compatible with the build on the PS3. Unfortunately (or fortunately) when you [put] games on [a] console you have a lengthy certification process to go through each time you release anything new." Hence, every time someone tweaked the UT3 build, it would have to be certified for the PS3 before it could be released for the computer. And since Epic has it's computer-owning customers closer to its heart than those owning a PS3, the PS3 was forced to lose the interoperability. On the bright side, though, PS3 owners still get access to all the UT3 mods and user-created content that PC users make.
Source: 1Up