I've seen wal-mart sell a few things a day (or more) before the item was supposed to be on public release. Nothing on the scale of the iPad2 but "Items" none the less. Heck, I think I bought John Mayer's "Where The Light Is" a week before the release date. Came back a few days later to grab a copy for my brother and it was missing.
Not apples to apples *pun intended? The point however, remains the same. If your local wal-mart has the potential to push the product I'd almost bet there is a person not paid enough to care about release dates/times putting it out. I'd also bet Wal-Mart wouldn't be the least bit threatened by Apple.