One very unique feature of Android and the Nexus 10 is the ability to have multi user accounts. Google knows that usually there is one tablet in a household, shared with everyone - unlike with smartphones. This feature was introduced with the new version of Android that came with the Nexus 10. And to show off that unique feature Google has released a new ad.
Who knows why Apple haven't implemented this on the iPad, it's a feature which has been requested ever since the first generation. But it looks like Google are the first to get there and are taking full advantage of it, and so they should be.