Well, the whole Rock Band thing has be a bit hesitant on Guitar Hero 3 (though if Rock Band turns out overpriced, that'll be a boost to GH3). I guess I'm more afraid of the franchise being treated like sports games, with a new incremental improvement every year. We'll have to watch how GH2 does being on two platforms, then I'd be able to say more accurately if 5 million over 4 platforms is accurate.
I still maintain the double-vote system should be around, though. There have been times where it would have helped.
This is a perfect case for a double-vote system on submissions. I have absolutely no issue with Guitar Hero 3 being listed (except that I should have done it myself!) but these IPOs are a tad high. I really don't expect the next Guitar Hero to pull in 5 million sales across all platforms, unless they had some massively awesome feature that got everyone to buy it. Especially since, as you noted, Rock Band is coming and it could steal much of the game's thunder on the PS3 and 360 (I'm under the impression that one's not coming to Wii).
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I still maintain the double-vote system should be around, though. There have been times where it would have helped.