See, it's started: http://blog.secondlife.com/2006/10/26/amazon-s3-for-the-win/
Ha! I was expecting to see this yesterday!
I won't rule out the possibility but it still doesn't make sense to me.
There are still huge potential legal, property, and tax liabilities yet to be explored with SL, one of the reasons why I suspect LL has no competition in this arena.
Amazon may partner with them as a service provider, and may back them as an investor hoping for future lucrative service contracts with LL. I'd hate to think that Amazon thinks they can do a better job of advancing this world.