I am so glad that bike manufacturers, both high-end and low-end, are making more road and MTB single-speed bikes for adults. This is so awesome.
Remember, most people with bikes aren't "Cyclist". They are just people with bikes. Just like most people with cameras aren't "Photographers", so why should they buy a full-featured camera when a point-n-shoot is good enough for the job?
Most riders don't need gears and lots of them have trouble with them either using them or maintaining them. How many times have you explained to a less experienced friend/girlfriend/whatever how to use gears. My favorite question that I hear is, "What's the best gear to use?"
I think that all bike manufacturers will have at least one single speed in their line ups soon. Yeah, they make more money on the geared bikes, but I think that more people will buy bikes that are easier to use and they'll make more money on volume.
Oh yeah, I don't want this thread to tarnish my Track/FG cred. Let it be known that I do ride Track. I ride brakeless. I do ride a track frame with all track specific parts (except bars). I ride in a big city. I got a bike crew. Word.