B612 wants to make a big telescope and put it in an orbit very far from Earth. PR's approach is different - make many small, cheap Arkyd telescopes and take advantage of economies of scale. They don't want to concentrate resources and risk in a single large object.
Building a small satellite is quite affordable, but commercial launch costs are a problem. There are several funded kickstarter projects whose goal is to deploy one or more satellites in orbit for much cheaper than what PR is trying to raise.
People also overestimate the difficulty of finding asteroids. Asteroids are still being discovered by amateur astronomers on Earth. It's estimated that there are millions of undiscovered objects. A big space telescope is an advantage but not a requirement.
other kickstarter projects:
http://www.kickstarter.com/projects/880837561/skycube-the-first-satellite-launched-by-you
http://www.kickstarter.com/projects/575960623/ardusat-your-arduino-experiment-in-space
http://www.kickstarter.com/projects/zacinaction/kicksat-your-personal-spacecraft-in-space
