I think the evidence shows launching first doesn't actually matter much. It's the games and the market perception.
For example Wii Sports made Wii an immediate sensation - the result was the console flattened 360 despite that consoles early lead.
360 sold okay but didn't really take off until after PS3 launched so it wasn't really the lead in the market it was the right games/services that made the difference.
Even launching two years ahead of the competition would matter little if the console didn't appeal and only gained a relatively small customer base.
Right now the Wii is dropping because globally it is less attrative than 360/PS3. So I'd say it's all about how attractive the console is to consumers - and maintaining that - that makes the difference. Launching first doesn't matter.
TBH I believe MS could have launched later and with a better console and I think they'd be even further ahead now : i.e. I think with hindsight their rush to market and the whole RROD cost them more than the rush to market gained them.
Try to be reasonable... its easier than you think...
