Agreed.
And this is why pollsters get things so wrong. Their poll is only represetative of those who took the poll. If a pollster calls me I instantly hang up, so my view is unrepresented.
As you say, the ABC is not a representation of all people, just those who could be arsed doing that test.
Polls used to be a lot ore accurate though, because they balanced for issues like yours and the ones I cited. The difference, so I read now, is that communications have changed with mobile phones and the internet, but polling practices and methodologies haven't kept up.