While the iPad has certain ecosystem advantages over the recently-released Surface with Windows RT, Microsoft's entry does of course edge out the Apple device in some key areas as well. One of them is its support for multiple users.
When you sign-in to an iPad using a surprisingly lengthy and complicated first-run experience, you establish a connection between the device and your iTunes account, which opens you up to Apple's media content and apps store. But it also binds the device to that one account. This is OK for many individual users, since it's their iPad and they're not sharing it with others.
But the Apple model falls apart in two ways. The first is a shared device. And let's face it, iPads—like the Surface—are expensive, so it shouldn't be surprising that many families buy one iPad and then share it between multiple people. But since the iPad supports only a single user account—that one iTunes account—there's no personalized home screens, email, calendar, apps, and games. Everything is shared.