Let's face it, quite a few people like shopping at Walmart because they carry everything: no reason to visit five stores, just one.Wait, isn't the iPhone at WM only like $4 cheaper? ($195 vs $199) so wouldn't the iPad only be a few dollars cheaper then???
Would there really be a point to go buy one at Walmart vs an Apple Store or BestBuy?
The savings add up. If you buy twenty items at Walmart with an average discount of $3, you've saved $60. I personally do not shop at Walmart, but this is capitalism. Joe Consumer shops where he wants to, and for many, that place is Walmart.
Remember that Levi Strauss almost went bankrupt because they refused to sell their clothes at Walmart (it's now a classic B-school case study). You go where your customers are.
Apple already has tons of customers shopping at Walmart (they sell iPhones, iPods, etc.). Selling the iPad there makes complete sense.