Guys, it's the LG Nexus tablet, it's NOT a new Nexus phone. There are still Nexus S phones expected to roll out to other carriers, Google isn't going to $h!t where they eat on this one. Also, they don't need to encourage people to develop for phones, they need people to develop apps for tablets. These giveaways aren't just for fun, they are there to drive developer interest.
I promise you, they are giving away Nexus Tablets to everyone at I/O. They'll probably show off new features to also get devs excistied, like an update of Honeycomb and some killer new apps (Gmusic). I imagine there'll be a preview of ICS, but the emphasis will be getting developers to make tablet optimized apps for Honeycomb.