The whole point of an ebook is to read them on multiple devices.
Another slight concern with Kindle is that I'm seeing more and more "this Kindle book is not available in Europe" messages from Amazon. Region coding sucked on DVDs, and sucks even more when you're not even buying physical media.
From a publisher's perspective, the point of an ebook is to cut down on manufacturing, storage, shipping, and other costs associated with a physical book. Since publishers own this game, I think we'll start seeing things get played increasingly by their rules as executives catch glimpse of potential savings in an ebook-dominant distribution chain.
And for Apple, it's a mechanism to lock-in, just like iTunes et al. Amazon doesn't have an interest in locking you in, so keeps books free, and has thus far been able to convince publishers that this is appropriate. Publishers may one day decide they can make double the money if people buy an iPad verison and a PC version, so I don't know how likely it is that Amazon will be able to keep that up.
No, they don't. There is not and never will be an OPEC of books. Publishers did not create the ePub standard. It was all the work of techies and book lovers who pushed for a standard file format. The Big 6 publishers are too busy fighting the future with their price-fixing Agency Model.