If PC gets too far ahead they'll pull the consumers (most frequent gamers and many casual) with them.
I think around 2011 would be a good time to reveal some ideas for the next gen, but not release them until end of 2013-2014.
PS2 was released in 2000, and PS3 in 2006. I guess you could say the PS2's life cycle was over after 6 years, but why are people still buying it 9 years later then? This generation hasnt reached anywhere near its peak, and we're already halfway through the PS2's "life cycle". Theres obviously more than 6 years worth in PS3 and 360.
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