What if All Your Books Belonged to Microsoft?

Or Apple. Some people might think the latter wouldn't be so bad, but my concern with e-readers is that the market will become dominated by two major companies. What if half the books you wanted to read were only published in a format that didn't work on your e-reader? Of course, they probably wouldn't do that now, but the more power the e-reader companies gain over books, what's to stop them from doing that or any number of other things, just because they can? Perhaps I'm just paranoid, but this is my concern with e-readers. I sincerely hope I'm wrong.