Minor comparison:
Nintendo cut the price of its Gamecube development kits later during the GC's lifespan (my search-fu is weak, it was between year 3-4 though.) Didn't make a dent in sales.
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This won't affect big developers, since they spend millions on developing games, and $10K isn't really a dealbreaker.
This will affect smaller developers, since development costs are much lower to the point where $10K is significant. Right now the X360 has a larger userbase though, and Wii Dev Kits are much cheaper ($2K.)
Right now, Sony has dropped the startup costs for PS3 indie games, assuming you wanted to make a X360/PS3 tech game and you couldn't decide between the two.