Actually, you make a really good point. Some of the TMI that is in person is kind of forced on us. But we don't have to choose to read a blog, or a specific entry if it doesn't interest us, so we can avoid TMI if we want. And lots of times people on my f-list will even label it TMI with a cut. So it's not intrusive.

And the reverse is true too - a lot of my work/IRL friends aren't interested in fandom and I don't want to risk boring them or having them fake interest in what I've got to say. But I can post it on LJ and it's much easier to find an interested audience or sympathetic ear, because it's voluntary on their part.