It does seem to be a bit of a fantasy standard. I have a RL hand-and-a-half (an Albion Gallowglass) and while I can't say how that fits into D&D's slightly esoteric categories, it's definitely not a small sword. But in spite of me not being particularly tall (5'7"/171cm) I can wear it from a belt with no problems: it doesn't drag on the ground, I can yank it out of its scabbard etc.
I have slightly mixed feelings about the subject. It's not realistic. On the other hand, I like swords so I like being able to see them, and while they're on my characters' backs I tend to get a better look. So there is that. And the swords are (so far) better done than the usual bejewelled spiky horrors that the fantasy genre is overly fond of...
