If everybody that's in college today manages to score one like this I'd be one happy fellow.
Nobody forces anybody to flip, it's all up to the people involved.
For instance, I keep sitting on http://langpop.com because I've grown fond of it, but I think it'd be worth more in someone else's hands. Maybe it would have taken up less of my time if I'd sold it off immediately after it got popular.
What Mark did is what 99% of the visitors here can only dream of, and if more of them manage to achieve it because of his example then that's the best possible outcome as far as I'm concerned.
It's just that there are more ways than one to achieve that goal and essentially by selling threewords.me Mark just made pretty good profit by selling a 'good' (threewords.me + the work invested) to a customer.
Why does everyone on HN ignore advertising revenue? Or is it lumped in with the above?