I think it depends if you whore yourself out.
For example, everytime someone posts on your wall... you get a visit. Each time you post on someone else's wall, or in their gallery, if they have manners, they will thank you by posting on your wall.
Those who are active in the gallery, have tons of people responding back.
Now, imagine you have tons of pictures and they are hot. People befriend you, and check your profile daily to see if you add. 100 friends x 7 days in a week =700 visits. Some of them check more than once...
It's a lovely game of numbers.