Who says you have to have an iPhone 4S to use Siri? The first video shows it on an iPhone 4 (which has been reduced in price since the 4S was released). Check out the rest of the vids too.
Siri enabled on an iPhone 4:
Another conversation with Siri:
A robot uses Android Speedcuber to solve a Rubik’s cube:
Robot ping pong:
Gary Vaynerchuck and Eric Ries talk “The Lean Startup”: