I've been thinking about this, and I believe there is a distinction since on the bus I am paying for the conveyance, not the content, so at no point do I ever consciously look at the advertising. For a magazine, I am consciously reading the content and they are putting advertising where my attention is directed. It doesn't help that the advertisements in a magazine pad it out so it looks like it has more content than it would otherwise.

I think that is more like a bus that detours to certain shops instead of taking shorter routes. You'd be paying for the conveyance and they would be abusing that by taking your time to gain themselves more money.