<quote>I see this a lot of HN, and I wonder if people are just assuming? To put it into context, I see far more ads on my iPad and iPad Touch than I ever have on my Nexus 5.</quote>I have zero ads on any of my apps on my iPhone (if I find one that has added ads, I discontinue it's use and buy another app that doesn't insult me). If you see any ads on your apps, you're buying the wrong ones.

If you mean website ads, then you can thank Google for that - I'm pretty sure that a significant majority of all web ads use Google's ad networks. Of course, thanks to Apple's double-tap for zoom, I usually bypass most of this visual cruft when browsing on my iPhone.