[John Scott]

Finally many of these themes try to legally disallow you from removing the advertising link by claiming it’s part of the Creative Commons attribution to leave it. This is almost funny, because these themes are on shaky legal ground themselves. WordPress is Free, meaning you’re free to do pretty much anything you like with it. It’s under a license that encourages user freedom called the GPL, which says if you distribute something that links internal functions and data structures of a GPL program (like themes do with WordPress) that also needs to be Free. At best, theme authors claiming you can’t remove the link are ignoring or ignorant of the license issues, at worst they’re actively exploiting the work of thousands of volunteers that have poured their blood, sweat, and tears into WordPress.

Great link, Cricket