That's what I said in comments on the page -- they could have gone for a mix of eBay and Humble Indie Bundle: offer what you want, and the best 100.000 get in.
Tweetbot is currently 2nd in the Top Paid and Top Grossing store charts, behind only OSX Mountain Lion. Those $1.4m will be in the bank in a few days. People didn't balk at the price one bit; I thought about it for a few minutes, and then went f#ck it, it's the only program good enough to make me tolerate Twitter, and devs gotta eat. I suspect for some power user, $50 or even $100 would have been fair game.