http://techcrunch.com/2016/02/10/mental-health-startup-lante...
http://techcrunch.com/2016/02/10/mental-health-startup-lante...
You can make 'world class' mean whatever you'd like, but I think most would consider Pitt a solid state-level school, whereas CMU is more competitive nationally.
http://dellweb.bfa.nsf.gov/awdlst2/default.asp
I'm definitely not saying it doesn't matter, but it's not as significant as CMU, and PG's argument seems to be that you benefit from having a really apex research institution for making a startup scene.
Pitt+CMU == complementary research institutions that have had a long tradition of collaborating (for example the Pittsburgh Supercomputing Center) and BOTH provide strong intellectual anchors for the city. BOTH are significant.
[1] https://en.m.wikipedia.org/wiki/University_of_Pittsburgh#Res...
Plus CMU and Pitt collaborate quite a lot, especially in biomedical research.