Well, if his customers get frustrated and move to another platform, he may have won the battle but lost the war. This is exactly what happened to TextMate; development was fast, at first, but then it slowed to a crawl and ST took over the market. I love ST{2|3} and am a fully paid member and I don't find it lacking in any respect. However, bit rot is a very real phenomenon and projects that can't keep up with the times are doomed.
Besides, going open source doesn't mean that you lose the keys to the kingdom. There are plenty of open source projects that make money; Linus is gainfully employed and he gives everything away. I'm sure there are ways to monetize ST beyond charging for binaries.