Well, jokes are never funny after they are explained, but i will shed my thoughts.
One way to look at it is that if you tried to correct everything wrong on the internet, such as blogs or Wikipedia, you would never get to sleep.
Another way to look at it is that the person on the computer thinks they are right about everything which is not possible.
Another way to look at it is that Sex is generally more fun than typing on the computer, so the person correcting people on the internet is inately wrong. I hope this helps. I guess with that being said, maybe the joke is not funny. But in my opinion it is.