They may have gone back and forth on what's in the box. The current listings on US Amazon show that the basic Kindle, the two versions of Touch, and the two versions of Paperwhite don't come with a wall adapter, while the three Keyboard versions and the various Fire versions do.
I had been thinking of buying a wall adapter, just because my Kindle USB adapter is extremely touchy and keeps ejecting and re-connecting at the slightest nearby motion, but my phone's USB cord isn't doing it, so I'll just stick with that.