Personally, I have always felt this to be true and I usually listen to music when I run (17:00/35:15). Personal favorite is Goa trance with BPMs from 120 to 140.
My brother is a more serious runner (14:45/31:15) and he only brings his mp3s on some long runs or on the treadmill when its cold outside. He says most "serious runners" don't listen to music when they run.