In open source projects, sometimes, if lucky, the more you give, the more you get back. So in some cases, whether one is selfless or selfishly motivated, open source may be a better model for many new and interesting types of projects than other structures.
I see this potential especially with creative complex projects. Where the best solutions only come from continuous synergy. It'd be in your best interest to keep participating, so selfless and selfish ironically becomes a false duality. Like being in a really good band.