Earlier quoted context omitted.
And questions which really are easy pickings will get 10 people answering them if the site becomes popular. So that $10 reward -- actually $7 after the 30% fee -- would have a 10% probability to win, assuming equal strength of answers for the really easy ones. I don't know many people who'd care about 70 cents.
It sounds like 10 people would care about it in that example you gave.
The first person responding perhaps thought it was easy money. Every subsequent answer is a race to the bottom. So why not go all the way and allow responders to underbid the last guy? That way, someone could spend an hour writing a very detailed response hoping to get the $7 and someone could come along, crib their answer off of the first one, and offer to accept only $6. The first guy, not wanting to totally waste the effort he put in, can then lower his bid to $5. Rinse and repeat.