Buying the Nexus 7 from Google doesn't just cost $250. Don't forget that they also charge tax ($25 by me) and shipping ($13 by me). Tax you get hit with at OD too, but not shipping. So this is a savings of $30.
That said, Androids have never been immune to price fluctuations like Apple is. Expect this new toy to drop later in the year. Don't believe me? Check SD for the history on the Galaxy Nexus phone, Google's last major release.