This is a super grey area amoungst themers

I personally dont care what sites my themes end up on,under whatever name,and as vinnie mentioned,if you watermark the theme,the end
users will know who made it and they are the ones that will go looking for more of your themes if they like them

On the other hand,some themers take great offence to seeing their themes uploaded to other sites by someone else,but personally i think most of these are simply uploaded for reasons of distributing the theme to a wider audience.
Its very rare you will see someone saying "Look at this theme i made" when clearly its your own.
The bottom line is....People that make themes for enjoyment and free distribution are getting exactly what they want right here....
1: Make a theme which you enjoyed doing
2: Upload a preview at m9
3: Sit back and wait for all the lovely comments to flood in

4: Look in the gallery and relax at the fact you uploaded and talked about your theme on the highest download site you are likely to find.
And no one can that away from you