This really is a false dichotomy. Being able to set different default apps isn't a huge thing to ask, doesn't alienate huge numbers of non-techies, and doesn't make an OS that does let you do so for tinkerers only or something. Conversely, asking for better UX for selecting which app to use doesn't imply that it's a bad idea that can only be serviced by a million knobs and buttons and so should be abandoned.
Thanks for pointing out the lack of precision in my preceding comment; by using the phrase "could offer" I erroneously implied a conviction that no such capability was possible. I've edited that comment, replacing "could offer" with "offered", to correct the problem.
