They don't need to do anything adversarial, the greed driven mindset of the internet (ads suck, everything should be free) staves off any real competition.
It's not nothing, but it's probably around 20%.
Also as others stated. I pay for everything, if they give me the opportunity to pay them for ad free versions. I don't see ads on my Android, and I don't use a general ad blocker on it (except my browser, but I rarely visit sites which would contain ads, and basically all of them from Hacker News). I don't use free search, email, newspapers, I pay for YouTube, and I would pay for Facebook if I would use it. I don't even use Hacker News freely, because I paid for the app which I use to not see ads, and have more features. Heck, I pay even for my torrent, because I support them.
You're in the wrong neighborhood with this sentiment. But yes, the general populace is not like this.
Hell the top story right now is about a tool for backdooring twitter...