There's some breed of horse from the far east I think that has ears that turn in like that. Beats me where they came from. :) Her color is different every time I walk out to the barn.
Hooked ears like that are fairly common and highly desirable in the gaited horse world. I don't know why, unless that maybe it makes them look "keener" or more intelligent, like they've got their ears pricked up all the time. Whatever it is, I like it.