[rquirk]

Substantial commitment is not necessary in practice. Joining the private beta of gaming.stackexchange.com required me to commit, but the site turned out to have a high XBox 360 and (surprisingly) Dwarf Fortress to everything else ratio and I have not returned with any enthusiasm.

I've outgrown games perhaps, but committing didn't require anything. Maybe if it had cost me 1000 Stack Overflow reputation points I would have thought twice about signing up? If it did cost that much, it would be a high barrier to entry for non-programmer-non-stackoverflowers and the site would get less people committing (resulting in the "ghost town" effect).