Only Apple brings you amazingly architected solutions like this.
This is precisely that "happy path or no path" mentality that I've complained about before. If you were green fielding a new OS, there's no way you say, "I know where we'll put the setting for the default mail app! In OUR email app!"
I mean, it makes sense if Mail.app is the only mail handler on your box. I'm guessing I can't delete it even though I don't use it, because if I could I wouldn't be able to select another client to replace it! I also bet the percentage of people using 3rd party email apps for their company email inside of the infinite loops is really low.
This is precisely why I wouldn't hate seeing Apple get split into a hardware-and-bios company and a separate software company or, better yet, companies. I don't hold out any hope for that... I think independent competition with OSes only happens if Linux ever finally commoditizes the desktop OS. Which is could do; I use Ubuntu regularly now. Which is also why it probably never will -- it's good enough for its user base, but still obviously not competitive enough for the typical end user.
In any event, Apple does a great job defining one clean-room use case for its products and, I assume, efficiently implementing that mvp. But it's not very creative at the next step: Coming up with potential real-world fail conditions once the mvp is running.