don't see how you can claim to be a professional developer if you're making less than 5K USD a year. Maybe if you worked in Lithuania or something but there's no way you could reasonably live off that little in Western Europe or the US.
I dont think the $5000 has anything to do with what people earn a year, its the initial shell-out of the readies that will concern some folk :)
The UK is one of the most expensive countrys in the western world, and your average joe, either profesional or not, takes a hit in the pocket every calendar month:-
http://money.scotsman.com/scotsman/articles/articledisplay.jsp?article_id=3628916§ion=Mortgages&prependForce=SM_
£2500 ($5000 roughly) is actually not very much money in the UK, but at the same time, its worth its weight in gold (unless your puki of course, but he lives with his mother, apparently)
I live on my own, I have a car and a van (both insured, both fully serviced and fully taxed), I have a mortgage (with insurances), I have Sky TV, I have telephone and broadband services. I'm fully up to date on my council tax and TV lisence. Water rates are paid as soon as the bill comes through the door, gas/electric is paid quarterly, and on time.
I go grocery shopping every week, I use the local milkman and fish man (cos you have to really)... And, I have a girlfriend that likes shoes (which woman doesnt) :)
Note, I havent got kids (well, I have a dog), and a lot of people do, and they are expensive to run (according to my mates)
So after all that, and if we take into consideration that £2500 a year as earnings is unrealistic, lets look at it at £2500 a month....
Which wouldnt leave me very much to play with at all after all the above is taken off. Luckily, I earn a little more than that a month and do have spare money, but I do know that a lot of people dont earn £625 a week net pay, and the average wage in the UK for blokes is (only, but still a decent wage) £564 a week gross!
The figures speak for themselves, professional, or not... $5000 IS a lot of money for people a year, its an extra 208 english quids a month to find! :/
Though, I am up for Blitz Research to do more premium content stuff on the site, dont get me wrong, I am very encouraged at the thought, but it'll have to be reasonably priced, much like, say, the creators club license for XNA or similar.
Cheers
Dabz