I'd say the same: it's up to publishers and authors to make their books available for non-Kindle buyers. If only because the Kindle is available to USA residents only...
Happily, there
are publishers and authors out there who don't rely only on Amazon and are already publishing .prc and .mobi ebooks. See the
Fictionwise or
Cyberread catalogs, for instance...
Edit: Not to mention
Mobipocket ebook store itself, of course !