I do think competition will be limited, though, as Apple's and Google's stores will be installed by default when you get the phone. Most people just stick with the default. Consider browser search engine defaults: Google pays Mozilla a lot of money to be the default search engine on Firefox, even with Firefox's small and declining market share. The holder of the default has a huge competitive advantage in that most users won't stray from it, or even think about the possibility of an alternative.

(It's funny, because this just feels like an echo of the 90s, when Microsoft killed Netscape in no small part by bundling Internet Explorer as the default for new OS installs.)