With text, I can get an impression of a post's value instantly. I think that's why Twitter works so well: unwanted content takes a second to scroll past.
Also, when I first arrived here, I saw the pic of the fish and assumed the audio would relate to aquariums or some such thing. Ewww. Boring. Ewwww.
I really love this experiment of yours, however. I didn't see the original post about it, if there was one, but as someone who works for Radian6, a Social Media Monitoring company, I think there's tremendous value in what you've proven here. I've always been aware of my own tendency to ignore audio or video content when I had no idea of the subject matter, but I thought it was because I'm very lazy.
Which I am.
Glad to see I'm not the only one that has zero patience on the web... I'm sure most people are in face that way inclined, it's just hard to prove!