In their CSS, they have a rule for every <p> tag to have "overflow: scroll" for some reason. Not sure why they didn't use the default value for overflow, since there's nothing on that page that needs to be specifically told to scroll.
We had a similar bug reported at work recently, and it turned out that Windows browsers will always show scrollbars but the ones running on OS X/iOS will hide them until you start scrolling.
To turn them on in OS X, go to System Preferences > General and set Show scroll bars to "Always".