I actually don't notice what you're observing.  When someone lets me out of a driveway I wave, and I think most do the same.  Sure some may not but it's not really a big deal.  I'm not so much concerned with what you state but rather with reckless driving that poses a real danger to those on the roads. If someone doesn't wave when I let them go it's no biggie but I wish death upon anyone who endangers my safety on the roads.