Have you noticed that iPhone/iPad app categories are less visible than they used to be in iTunes? If you go to the top level of the App Store, you won’t find categories there at all. They are still available. One way to look at categories and their Top Paid and Top Free apps lists is to select an app and then click/select its category in the upper left hand corner.
However, you’ll find it is simple to search for apps in a particular category on the iPad itself. One of the four options in the selection bar at the bottom of the screen is Categories. Tap it to search for apps by category. Unfortunately, the iPad categories pages do not list the top paid and free apps.