The ads you're referring to here are called display ads. Most of these ads are not about getting you to click, but about awareness.
It's the same thing as a full-page advert in a magazine that you flip through. For some readers, they will stop an read it, raising awareness to that brand/product/company etc.
I take your point about being "exposed" to the product, however it must be the case that ads want you to click them, otherwise clicking them would not do anything. Which is not the case.
A company spamming my eyeballs with visual ads to "raise awareness" does not get my money. I take particular offence to that, as it is my screen. Not a Billboard for example.
My point is proven in the HN website, where it enjoys a large readership, largely influenced by the sites clean, ad-free design.
Slashdot used to be like that until they started displaying ads, and that is what brought me to HN. Thank you HN for not doing this.
It's the same thing as a full-page advert in a magazine that you flip through. For some readers, they will stop an read it, raising awareness to that brand/product/company etc.