I guess the important points are…
A) The average theme makes $12,000 a year… don’t make an average theme.
B) Who is going to make a theme that makes $12,000 a year, give up their job, and just sit around doing nothing for the next year? Other than the support requirements that go with it, obviously. If you’re making $12,000 a year and that’s not enough for you, then you can 1) Get a job, do support in your spare time, and get an extra $12,000 a year on top of your salary, or… 2) Make another theme!
C) I hear that an average theme usually takes three months to create. I could be wrong, I’m no theme wizard. So although you may get $12,000 in a year, it could be said that you’ve also got $12,000 for three months of work… or $24,000 in the second year, $36,000 in the third. Although you might not be buying your own tropical island on that, $36,000 for three months of work isn’t too shabby.