How successful are all incubators? Universities have disadvantages, yes, but also advantages, depending on the sector. If you need lab validation (or discovery), no place better! If you need cheap but highly skilled workers, try grad students.
Any place that tries to encourage lots of startups is going to run into the same problems -- university or no: concentration of skilled workers. Sufficient top managerial experience in the area. Access to capital, startup-savvy accountants, lawyers, etc. So a university in the boondocks, just like any other for-profit in the boondocks, is going to have a tougher time than one that has a well-developed cluster around it.
The answer about patent skills is true of all patent attorneys, not just universities.
For actual statistics, go to http://www.nbia.org (natl. business incubation assn.), autm.net (Assn Univ Tech Managers -- really tech transfer officers) and perhaps aurp.org (Univ. Research Parks).