Cant talk for the US, but would have to agree with the talk about instructors in Europe. As a student myself, I have the oppurtunity to have a quick chat with a fair few instructors. General consensus seems to be similar as to what is said here.
Another point is salary; to fly 800 hours per annum could be a pretty draining experience, working out about 15 hrs a week if my maths is right, assuming 7 days a week available, complete other story if you want part time. For EU guys I believe average for PPL instructor is about 20-25£ an hour.
What with paying off flying loans, general up keep e.t.c it must be extremely difficult to keep your head above water. Not sure if the situation is similar in the US, but it leads us to a pretty bleak conclusion either way.