My experience is the opposite...hearing is so useful that I typically don't run the radio in my car and I like to drive with the windows cracked. I can often tell if another car is in my blind spot just by hearing it. I find this actually gets easier the faster I'm going.

I think it depends on personal experience. I had a car without a radio for years (stolen, too expensive to replace), so I got used to hearing the traffic around me. For the short period of time I bike commuted this translated really well. But if you're not used to using your hearing that way I can see how it would seem useless.