I don't think so- but that's just your feeling, and I totally understand.
There are people I see all the time when I'm riding, and some of them give me no thought whatsoever. Others say hi, or good morning or whatever. I try to nod or make eye contact with everyone I see, and if they're looking receptive, I'll give a gesture of hello or whatever.
I also stop anytime I think someone needs help. About a month ago, I saw a woman go down hard, and she was bleeding out of her nose pretty bad. A couple of weeks ago, I guy took a bad tumble over that big assed crack over by the museum campus and went over the handlebars, and I pulled over for him. Then about a week ago, I met a nice group of people that were stopped because this guy was making repairs to his recumbent bike and I wanted to see if they needed help. I try to stop for everyone that looks like they need the help, and I would hope they would stop for me! What comes around, goes around, I always say.
I don't personally get annoyed if people don't say hi, but if you think you'd like to get a nod or something, maybe you can be a little more "aggressive" (for lack of a better word) when saying hello. If they're still ignoring you, they're not worth the time. Then again, they better never have problems and need help either, because if they are not friendly to most people, and those people pass them by when they need the help, they have no one but themselves to blame!