The holy grail of safe operation in same space as humans, and affordability. Those involved in robotics quite rightly point to all the other robots that are capable of this to a degree, however the true significance is the scale at which Rethink Robotics has achieved this.

Rethink set clear goal posts fairly far out, acquired big VC backing, created market expectations, ably fueled by marketing materials, story, website etc all promoting the next wave of robotics redefining manufacturing and bringing better jobs.

Rodney Brooks tells a robot story like a superstar - he's responsible for the renaissance in space exploration with robots with his paper "Fast, Cheap and Out of Control" back in 1987 and subsequent work on Mars Rover. He also championed biomimetic robots with only enough intelligence to do stuff back in the days when AI was the holy grail, leading of course to Roombas and a significant shift in robotics design (which also leads to cloud robotics).

So, in short, others might also be doing what Rethink is, but Rethink are 110% selling us the story as well as the robot. (including rebranding as Rethink Robotics from original company name Heartland, spawn of iRobot)