Complaining about the rain is the same as people complaining about their jobs. It's just something to complain about. When you really can't tolerate either, you usually do something about it.
I don't mind the rain (which isn't to say I've never complained about it) Like Sportsdude says....that's why everything is lush and green. And it certainly beats some of the things that people tolerate.
Earthquakes, tornados, hurricanes, ice, snow, bitter cold, floods.........rain sounds like the most tolerable of all. I can't imagine trading off a little rain for any of the other 'options'.