Specifically on the exit stats GrabCAD (Boston TS company from 2012) was acquired for 100 million -
http://betaboston.com/news/2014/09/16/product-design-startup...
And the real answer to this is that getting large exits takes a long time. Unless I'm mistaken YC, which is older than Techstars and has 50% more portfolio companies, has 3 exits over 100 million, OMGPOP, Heroku and Twitch. Granted the last one was a big one.