Just looking at Trek's and Specialized's web pages, it seems that there aren't really hybrids any more. There are "fitness", "dual sport", "utility", and "city" bike categories. Within those categories might be one or two bikes that resemble what I think of when I hear the term "hybrid". And usually, they are the cheapest models. For the most part, the fitness bikes are like flat bar road bikes, and the dual sports are like hard tail mountain bikes with less aggressive tires.
As far as comfort goes, it really depends on what you're doing. I might find a cheap hybrid with a cheesy front suspension more comfortable on a really bad road than better bikes without a suspension. I can ride any bike for a few miles and be comfortable enough as long as it's adjusted correctly. I imagine most people could unless the few miles involves some big hills or they are just really out of shape.
I'm not sure how you feel about the local bike share bikes Cranky but the only adjustment on those is seat height and people seem to manage with them. I don't know how close they are to hybrid geometry or something else. I wouldn't want to tour with one but for trips of a few miles (what they are intended for), they're fine.
If people ride a few times a year then I see no reason to spend $500 or more on a bike and it shouldn't be surprising that Americans would buy a lot of cheap bikes. Would they ride more if they had better bikes? I do think there are people who ended up with a bike that they just don't like and would ride more if they had something different. I'm not sure hybrids are any more likely to be the cause of people's lack of interest in cycling than any other bike.