FWIW (free, you get what you pay for, blah blah, etc.), in other areas of the law, knowingly allowing someone to commit a crime, or violate a contract, means that you have given permission for that activity and as a result any future case you file in court or otherwise try to prosecute can become much weaker. Trademarks are one example.
So, the longer they knowingly wait to prosecute, the thinner the ice gets, so to speak, because at some point they are allowing it to happen. A risky strategy on Altium's part, perhaps? Someday they will hit someone who is itching for a fight or feels that they have little to lose.
It seems to me is that this kind of activity is certainly going to alienate some portion of the userbase. I know for sure that if I were a consultant or independent business and absolutely needed Altium, I would save every scrap of info I ever got from Altium and ask them for written clarification on every little thing in their contract that I didn't understand. It puts the ball in their court, so to speak.
It's a shame, really. I wish they spent the money on making the tool better. I mean, engineers seem to be cheaper than lawyers these days. They are probably run by some pinhead MBA at this point...