I can think of a couple of reasons:
1) Nobody needed it when outlets weren't grounded or we didn't have wall-warts;
2) It probably still isn't legal in kitchens where outlets are "split"- two circuits to each plug;
3) Because it is made by one manufacturer and is different than the universal standard, it probably costs five times as much;
4) It probably took five years and hundreds of thousands of dollars to get all those approval labels stamped into it;
5) I notice it only has one screw on the side, so it probably is only legal if it has its own breaker.
That is the problem with so much of design- you can have the great idea but the system, the codes and the "way we always did it" grinds innovation to a halt. Designers don't just need an idea and talent, they need guts, persistence and money. Or be named Starck. ::Materialicious via::BoingBoing