One could argue that the whole point of ads is to draw your attention and put things into your memory, which is not necessarily the case for those other things. Some radio programs probably are meant to draw attention, but you could notice this and switch away, which brings us to...

> Where does the line get drawn?

Ideally by the person who knows most intimately how badly you're being distracted, i.e. you. (Until they get the ability to scan your brain.)