That would be what the LiteStep license says...however...did you read the GPL beyond that? The part where it says you have to offer the source or at least tell them where to get it?

Themes on the other hand are not covered under the GPL they are under what I believe is creative commons. Which means you need to give credit to republish or redistribute and get permission to modify anything. Just because non|step has not been developed doesn't give you free reign with it. (ie. the copyright never expires)

Serial numbers are still considered cracks because the software was cracked to get it. It is illegal to bypass restrictions on software in this manner. It is called software piracy and you can go to jail for a long long time for it. As for forum rules against it...check the footer of every page on this site. Under those rules you can be removed from the site...but at the moment I am feeling generous. xcal can attest to how rare that really is.