I think that the popularity of Chrome and the usage problems that occur because it can't be set to default have merely started the conversation. It isn't just Google apps. Sparrow, for example, is a top notch email client. It's tough to use exclusively because many of the email features embedded within iOS point to the Mail app instead. As third-party applications continue to increase in quality and functionality over the stock apps, users will likely prefer to change default apps. Apple's job is to make users happy.