My team colleague and, now, partner in crime, Udo Szabo, sent me a great quote (see below) that sent me looking for the full article on the Google blog, and written by the guy who brought Gmail to life.
Basically, they entered a really mature market and redefined what Web email should be like. Yeah, free 2GB email was a hook, but that's part of the product strategy, the benefit to users, and the basis for so much more that they've added since (contextual ads, FedEx links, integration with Google Calendar, and so on).
To me, it says that a mature market is only mature because the innovation has stagnated, the mind-set has gelled, creativity has fled to easier problems.
This whole thing also makes me think back to ideas about the 'freeing' nature of constraints in design and stepping back a bit and revisiting past aussumptions, thought to be immutable, upon which we built our current assumptions.
We didn't want to simply bolt new features onto old interfaces. We needed to rethink email, but at the same time we needed to respect that email already had over 30 years of history, thousands of existing programs, and nearly a billion users. So we started by learning which features were most important, and which problems were most aggravating. We also realized that solving everyone's problems was too big of a challenge for the first release. It would be better to build a product that a lot of people love, than one that everyone tolerates, and so that was our goal.