I don't think that's the factor at all in that case. If buzz and twitter were launched at the same time, twitter would win. Buzz did too many things wrong - privacy, being integrated into gmail, not as open API etc, no arbitrary restriction on length to get hype, etc

Plus, being launched by Google, may actually be a curse. I doubt the xbox would be as successful if more people actually knew microsoft was behind it.

Startups have a great advantage in that they're assumed by users to be new/fresh/good guys/underdogs/etc etc