Hi there - your theme was set to use the Infinite Scroll setting, which overrides the setting for a particular number of posts per page, and allows visitors to simply keep scrolling to see all your posts.
I turned that off under Settings > Reading - by unchecking "Scroll Infinitely."
Your blog homepage now shows four posts.
You can learn more about the Infinite Scroll feature here:
http://en.support.wordpress.com/infinite-scroll/
If you need anything else, just let us know.