I deal with this occasionally at work, since I work in sales. Customer buys something for normal price. Later down the road, the product goes on sale for one reason or another, customer finds out and gets pissed, thinks we're just trying to screw him over.

Doesn't matter what the product is, if a company EVER puts it on sale, there will always be someone that purchased it previously at the regular price. That's what a "sale" is - selling something cheaper than it was previously sold for. That's awesome that they refunded you the difference, but even if they hadn't, I just don't understand getting angry over it. It's just business. To get mad over that is totally irrational.