It's not a myth, the numbers do not lie. By far the hardest game to win on the road. Along with other sports like traveling (however sports like football you usually travel days before and settle in) and home field advantage, I would imagine the most common reason would be shooting difficulties and the differences in arenas can play tricks on you.
http://rpiratings.com/homecourtrec.php
Oh and this http://sports.espn.go.com/ncb/news/story?id=4682821