Wouldn't really call it a sale. If that's the case I got mine on "sale" back in May from MacMall.com as I didn't have to pay tax or for shipping either.
As for why purchasing from any of the listed b&m stores, well Apple does offer the refurb for less and if you're a student, the discount available does help take a few bucks off.
BestBuy offers a trade in program, so you can trade in older electronics on their list to help bring the cost down. Something else to keep in mind, now that Target and BestBuy carry the ipad, I can expect to see some competing offers such as gift cards or bundled accessories to attract potential buyers.
Amazon is still a good option though, provided that it is Amazon and not a 3rd party supplier.
Something else I forgot, if you're a reward zone member for BestBuy, even a 16gb wi-fi model is already enough for a $10 rewards cert.