I've never read hard numbers on this, but it wouldn't surprise me if that is true. Even I have an open source system that I built for somebody, who's not actually using it. I keep telling myself I'm going to clean things up just for the heck of it, but I have yet to touch it since last year.
It's been my impression that new technologies go through a lot of boom and bust, and I wonder if that's where some of this comes from. You write something in a hot new language, but two years later nobody cares about it because that technology actually sucked.
FWIW, I try to think economically about the technology I invest time and learning into. I really don't waste my time with the bleeding edge, as established technologies that show signs of being around a long time have a higher ROI, in my opinion. However, if you gamble your time and get lucky, certain new technologies take off and you get to be one of the few people with the most experience. Not a bad way to make big bucks, but you have to get a little lucky. Kind of off topic, but oh well.