I don't know how typical it is, but I don't think it's unusual. It's certainly not a phenomenon.
People have pointed out that my post count is way to high to have schizoid PD. I think it's a symptom of it for two reasons. One is that just because I am alone most of the time doesn't mean I don't have anything to say. I don't post on other forums much or use social media because nons annoy me. Posting here allows me to express myself and get stuff off my chest. Face to face communication is daunting because it requires relinquishing my isolation and I can't control it the way I can when I'm communicating online. many times I'll be making a post, suddenly become disinterested, save the draft, and come back to it later. Sometimes a few hours later, sometimes a few weeks. You can't do that in social situations. Well you can but it doesn't go over to well.
Reason two might be that I don't consider verbal communication and text communication to be at all in the same arena. If you're younger than me and grew up with a phone or tablet on your lap it's easier to equate the two, but that's a mistake. There's no way that facial expressions, body language and tone of voice can be properly replicated with text. You're missing half the picture. But it happens to be way more comfortable and convenient for me.
Your being an English major definitely has something to do with it. I like to write. I like the english language. So many ways to say almost the same thing, but with all those awesome words that enable you to tweak your meaning so that you can get your point across succinctly. I agree, it is fun.