I can't deny I did the same, but there can be a psychological effect here in that $40 is unpalatable as the MSRP, but when it's $50 on sale at $40 then it suddenly becomes easier to swallow.
But like said, I don't mind too much. Not only is there the "we've been paying $30 for twenty years!" angle I brought up, but most of the rest of the world HAS been paying $50+ for handheld titles for a long, long time. And unlike optical media, carts are not cheap to produce (it's even cited as THE reason it's $50, the fact it's on an expensive 4 GB cart), so it really doesn't seem that unreasonable to me as long as either the production values justify it or it's so niche a product it's the only way to make a reasonable profit from it.