Because evil robots aren't going to build themselves
The childhood building sets of yesteryear were somewhat limited: K'Nex could only produce skeletons, while the kids who wasted away indoors playing with Legos ended up looking even grosser. See just how crazily far things have progressed, with Cubelets.
Just now available for re-pre-order after selling out their beta run near-instantly, Cubelets -- built as the Carnegie Mellon Ph.D. project of a Boulder engineer -- are a kit of 20 combine-able magnetic blocks "that can be snapped together to make an endless variety of robots", meaning they'd absolutely kill it to a mastermix of Chris Brown on America's Best Dance Crew. The blocks are categorized as: Action, which include ones that'll wheel around on flat surfaces, rotate in place, or flash a light; Sense, which can detect things like light or temperature (of the room, your breath, or whatever); and ones that only act in tandem with others (e.g. one that "flips the values it encounters") called Think Blocks, or what David Carr used to futilely plead to his o-line. The fun's in stringing multiple blocks together: combine "drive" blocks with "distance" ones, for example, and you've got a robot that'll chase down the objects it senses (adding "inverse" Think Blocks will result in a robotic scaredy cat); hooking up the same drive blocks with "brightness" sensors creates an automaton that'll doggedly follow a flashlight's beam, making them perfect to unleash on someone with super-boring ghost stories.
For the serious machinist, buying and combining multiple 20-piece kits opens up the possibility for even crazier tinkering, like a set-up that'll shine a mirrored display of your own hand if you brush across it, or one that'll function as a roving flashlighting security system -- something far beyond the reach of classic Lego sets, though not even robbers wanted to visit those kids.