But Gmail does support non-gmail accounts as well. You could argue that it's easier to get a Gmail account than to install yet another application on your iPhon

But Gmail does support non-gmail accounts as well. You could argue that it's easier to get a Gmail account than to install yet another application on your iPhone, not to mention that Gmail will continue to be free for the foreseeable future. At first glance it seems like you have a product that could be interesting only to Apple, if they can't easily add the functionality themlselves and the build vs. buy math works out.