Without actual data to back it up the argument that "there isn't enough RF spectrum to handle everyone at once" sounds fishy to me.
When I was in Beijing for the summer of 2005, local wireless carriers would bring in extra portable towers to areas that expected to have more people than usual. I was on a college campus (Tsinghua) and we saw the little trucks with their portable towers pretty often whenever anything was going on. None of us ever had any problems ever, and here is the kicker you probably didn't know: there are a lot of people in China! And the population density in Beijing is really high! (sorry, sarcasm is annoying I know).
I realize that now in 2010 people use more data so it is harder to keep up...
...
but on my last trip to Hong Kong I was talking to my friends there and asked how often then get data problems or dropped calls with their iphones. They honestly didn't know what I was talking about. My friend said "oh yeah, I think I had a call drop about a year ago when I was talking on a long call while traveling" and someone else mentioned getting really slow data at a big concert.
I think that US cell phone consumers just have been convinced to maintain low standards for quality, the way the FCC distributes spectrum is a huge mess, and it is hard enough to switch carriers that people can't really vote with their dollars. So to everyone saying "this is just how it is, accept it" I wish you could at least have the decency to be a little frustrated and demand more.