I have no doubt that GTA will head to the WII. Give it time. In the moment they couldn't announce that without pissing MS and Sony and may hurting their GTA 4 sails on both systems. Heck GTA 4 PC is not announced yet, but will properly come sometime.
I say GTA is coming to the WII in the time from Aug. 08 - Sept. 09. Depending on how got its selling on the other systems and how long it takes them to do a engine which looks similar (for the programmer, not the graphics) to their existing one for GTA. They may need to "downsize" some things, but there is plenty money on the table for them if they do. And Rockstar is not that stupid not to get that.
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