Do Americans really just hang up the phone without signing off?

I see in American TV and film that sometimes they just put down the phone without saying 'goodbye' or anything. I would find this to be VERY rude. Is it only cops and heroes that do this or is it normal?
Update: Hi Mike, yeah, I know Yanks are as polite as they come, this just seems odd to me hanging up without signing off. Im sure every culture does something that others would consider rude.
29 answers 29