It goes back to what Sith says - if someone puts the time and effort into making it, and they want to charge for it, and someone wants to pay for it....then no harm no foul.
If someone wants to provide them for free, that's their perogative, too.
I have only attempted to make a theme (a long time ago), and I am not sure I would charge for them. At least at first - since they might not be the best quality.
There are other themes that are quite polished and I think they are well worth the $$.
No longer a BES Admin, but it was fun while it lasted!