Isn't this a license violation?That depends. If people who buy "their" software get the modified source along with it, and it's also under the terms of the GPL, then they are compliant AFAIK. They can also just put up a link to download the source, but IIRC, that's not required if it's shipped with the CD (or whatever kind of media they are distributing).
OTOH, if they are really complying and releasing their patches under the GPL, you could spend the $19.00 to buy one of their distributions, then turn around and put their patches back into your base software if you wanted to.
