Model release and holiday?

istockphoto said that:
When do I need a model release?
If the images that you are submitting have an identifiable human face, then you will need a model release.

Other sites are similar.

Now i have a big question there are situation for example holiday where it's possibile photograph people with particular dressed (for example medieval dressed) i don't think it's necessary model release or i'm wrong?

Naturally i said when i would like sell the photo.

Bye Alex