But it is mostly true.
However, there are other cyclists, who you would think would be like the walkers, gardeners, porch-sitters, etc. The kids on bikes are a little leery of talking to stranger adults, so I don't try -- I just wave and if they want to start a conversation, I'll respond, but I don't push it. The adults on bikes with kids (on a trail-a-bike, or accompanying a trike or whatever) are also fine -- if you pace them, you can chat as long as you want to. The adults on bikes in spandex, however, do not so much as respond to a hello and a wave clearly directed at them. They do slow down (because T. is not totally predictable, this is the correct thing to do), and I do thank them. They give me a blank or angry look and continue on. R. thinks this is just because on a bicycle, you can easily get into a identify threat deal with threat identify threat deal with threat etc. mode.
I would just like to note, however, that that's kinda bad from a community perspective. In fact, the only thing less bad about this than the people in the sealed up cars is that the cars weigh a lot more and can, basic physics, do more damage to us without taking damage in return (unfair hunting, in other words).