I viewed Google I/O, Jelly Bean (Android 4.1) and the first Nexus tablet as Google's last chance to deliver a knockout in the tablet space before the onslaught of Windows 8 and Windows RT devices later this year. While the show was undoubtedly a success, I don't know that the market for $499+ Android tablets has a life after Windows 8/RT hit. We should see Windows RT tablets at $499, and Ivy/Haswell based Windows 8 tablets will handle the higher price points.
It seems that Google also realized this as the Nexus 7, its first Nexus branded tablet, starts at just $199. There's a huge market for tablets as a primary computing device, and I believe Windows RT/8 offers something unique and compelling for that usage model. At the same time however, there's decent demand for a tablet to augment your existing computing world. It's a far more specific usage model but one that really demands a lower price point. Users are willing to spend a lot for something that does everything in your life, but for something that's more nice than necessity, price matters even more.
The Nexus 7 is aimed at the latter. It's a device for users who need ultra portability and tons of battery life for content consumption. While Apple has been quietly empowering the iPad to be a content creation device, and dockable Windows 8/RT tablets will attempt to replace your notebook, the Nexus 7 is a more traditional ARM based tablet by default.