I have to tin-foil-hat this one and ask: Is it hard to prevent or do the developers just not WANT to prevent it? What profit incentive does MS have to fight the marketers who are constantly abusing their code? And does the Mozilla community have time to fight this battle?

Google, on the other hand, is more than happy to further ingrain their name into your every fabric of existance via a solidly working popup blocking solution. Just like so many other software tools/utilities, let third parties profit from solutions that the big boys don't want to fix/implement.