Because they are curved swords. CURVED... swords.
Of course.

I blame
Highlander and all the publicity about how strong the steel is (the million foldings to increase the density). Plus, the YouTube video of a katana blade slicing a fired .50 BMG bullet doesn't help.

In games like Fable II wherein the various swords have differing damage to speed ratios I get it, but usu I suspect it's the look and the exotic nature of them.

Edit:
Seems to be a fad where teens (more American, really) are obsessed with 'Japanese culture' through watching a few animes/mangas, even though it's nothing at all like their culture.
This too.
