Yeah. That's not a problem. The law isn't to prevent the infringer from gaining, but to prevent the copyright/trademark holder from losing. They still owe the copyright holder for damages done (assuming they're found to be infringing).
Right, and the current number of users they have are using their program, instead of something made by the original copyright holder, because they (may have) violated copyright. It could be argued that all past, and future, income was derived because of their copyright violation... Also, in civil court, you only need to prove the possibility that this is the case.
The UNIX philosophy basically involves giving you enough rope to hang yourself. And then a couple of feet more, just to be sure.