And what, pray tell, is Vex? Imagine building your own robot from Erector-esque metal girders and plates. You get to learn about how the gears work, configure tires (rubber tires or plastic treads, small or large?) and program the microcontroller to obey your commands. Everything about Vex (particularly the Vex Robotics Starter Kit) is optimized for educational users. (Pure hobbyists might prefer the Vexplorer.)
Geekdad has a pretty awesome article about VEX and they even link to the video I edited of the Vex Walker. I don't know when the Walker will make it to market but it will be cool when it does.
The Vex RCR Mini should be on the market in August and it will be a seriously cool kit. The Mini beams have half the hole pitch of the regular Vex so it will be easy to build a bot that is half the size of the Vexplorer.