That theory would be an accurate reflection of my life experience...I've never met a person who uses Reddit IRL. I know people use it and that it's popular, but I just don't know any and I've never met any, so I'm biased toward the belief that most conversations on reddit aren't being held by people.

I have heard of that, and I think that's accurate for a lot of mainstream sites. I'd go a step further and say they have different "categories" of the internet that they sort you into based on your "profile" online, whether based on geographic area or search history. So depending on where you live or what arbitrary "category" they put you into, you might see a slightly different internet from everyone else. Don't have any real evidence to prove that, just a gut feeling.