I think mostly people on HN are interested in making apps that provide real value to users and business for the long term.
Some people just want to get 2 months pay for 1 month's work and make they an iFart app or whatever to achieve that. It's not a long term bet but it makes more than being employed - for some people that is all the care about.
Also, the OP talks about companies being founded but I would guess in most cases Facebook and iPhone apps are people side projects made in their bedrooms or instead of doing consulting work. Those people are realistic and don't expect it to last, it's just a way to make money in the short term, they'd leave if there was more money to be made elsewhere and will probably leave anyway as the race to the bottom plays out.
