I wonder if this has anything to do with Amazon's new 70% royalty rules which state that any book offered at another bookseller cannot undercut the Amazon price in order to qualify.
And while it's nice that Kindle users can get syncable versions of these books free, I hope Amazon doesn't make a habit of it. Considering just how many Smashwords books are out there, it could quickly become tedious to find the new time-limited special promo freebies*.
* Cf. the current state of Inkmesh's Barnes & Noble free books list.