Don't bank on VCR either, since Macrovision (the main protection used) applies to them as well.
The oldest versions of Macrovision were simpler, consisting of deliberate disturbance to sync and black level, compensated for by the circuits in most TVs (and some older VCRs). Later VCRs had their sync and level stabilization deliberately weakened, so were unable to correct for the disruption.
Later versions of Macrovision apparently also include a digital component, some form of signalling to reinforce the analog disruption. Older forms of macrovision removal may not remove the digital signalling.
At it's simplest, the old forms of removal just had to emulate the way a TV handles the signal, with superior sync stabilization and level clamping.
As with any form of protection, it is imperfect - I have seen TV's that are disturbed by it (in one case, would not operate correctly over RF, but ok when SCART was added). It is also quite common for TV/Video projectors to have problems.