I think because the event was for the launch of the Galaxy Nexus and ICS, not just ICS, they just focused on the OS as it will be on the Galaxy Nexus. It wasn't just a Google event, Samsung was revealing hardware that they hope can bring in some serious dollars. I don't think they wanted people to lose focus of that. The plan was always to integrate the phone and tablet aspects of Android with ICS.
I saw this site too, one complaint I have is all the pics show the back, home, menu buttons with the black border going across the whole bottom of the device. If this is how ICS on Tabs is going to be, then we just lost some screen real estate. I would much rather see wallpaper, than a black bar across the bottom. BOO to this feature, and I thought I liked it on a phone!