amazon does not want drm, they want to sell books, and most publishers wont let them do that without drm. IF they see epub as the way to sell more books, while still keeping the publishers happy. I'm sure they will do it.
but their ultimate goal I believe is books without drm. but if epub becomes universal, than drm doesn't matter. because then your drmed epub can be read anywhere.
all they need to do it have every other Ebook reader come onto the market with ADOBE epub drm support. and then they may switch to Epub.
but currently. they seem to be selling more than enough kindles and kindle books.