Angry Grimace
Two cannibals are eating a clown. One turns to the other and says "does something taste funny to you?"
The anime and manga fandom exists more on message boards than it does in real life, however, so the population not using message boards argument doesn't really apply here. Anime and manga are dead markets outside of Japan right now and the majority of people who are viewing these products are pirating them aka we have absolutely no real measure on how many people are actually anime and manga fans in the West. This is why you absolutely cannot use buyrates and sales as an argument cause it's missing more than half of the fandom's opinion that exists on the internet. This also applies to the piracy that happens in Eastern countries too.
When it comes to opinions on anime/manga, message boards is all you got as a weight. There's positive opinions too, but going to the average message board when bringing up a series like Naruto and Bleach in a topic will just get critical lashings about how much the series suck.
Like I said, if there was a legitimate site that criticized anime and manga properly, both of these series would be the lowest on the totem pole when it comes to popular shonen series.
You're confusing "people with internet access" with "people who post on message boards."
Just look at the comment section after every chapter, dude. Its not all people complaining, that's just what you go looking for.