If you're working at these companies you also know they have lots of people like you who will be working to track down any trace of who leaked the code. Are you willing to risk going to prison then being legally banned from touching a PC when you get out?

Also, you have little to gain from doing it even if you don't get caught. It's probably much more cathartic to blast them in a blog post than it is to anonymously release source code of an outdated/discontinued product. Especially since source is only readable to x people and a blog is readable to y. With X<<y.