Scott, another thing to note. A large part of Amazon's numbers are public domain books that are available for free for the Sony both here (MobileRead) and from other sites. Amazon charges for those freebies.
(PS: I, too, received a Sony for Christmas and when my wife said she thought she would buy the Kindle for me rather than the Sony I had been hinting for, I told I was pleased she opted for the Sony -- it meant I didn't have to go through the hassle of returning the gift
)