I'm going on the angle of why they allowed their code to exist out in the wild. Freeware, shareware, etc. It's done for a reason.
It's their name on it, it's their brand mark, and free advertising for them. It is very much potential income.
Taking somebody's code, mucking with it, or calling it your own without proper attribution is quite similar to plagiarism on one's term paper.
Oleg had to go after folks stealing his images and using them on anti-gun sites.
I myself had to get into someone's chili on Auction Arms, because the rifle photo of the gun they were auctioning was lifted from my image collection, leaving my watermark in plain view.