PA has been described by many as, "Philadelphia and Pittsburg, with Alabama in-between."
I'm guessing the reason why those two cities are used are not only because of population, but because people (from my own personal experience living in Pennsylvania) really don't know where anything is at on each side of the state (East / West).
You ask a local in NC where Asheville, Boone, Greensboro, Burlington, Hendersonville, Raleigh, Durham, Fayetteville, Greenville, Wilmington, Outer Banks, Emerald Isle or Cary is, there is a good chance everyone knows what area your talking about.
Go to Pa and ask a local where Washington, Erie, Reading, Scranton, Upper Darby, Abington, Altoona or Meadville is, there is a good chance people might get some of the cities/towns on their side of the state, but in general, most people on the East Side of Pa might know where Pittsburgh is and people on the West side of the state might know where Philly and Harrisburg are at, but after that, you'd be pushing your luck.
Even when I lived in central upstate NY, people in the state seemed to have a better comprehension of where cities and towns were in the entire state vs just one side vs the other side in the state.
I could be wrong, but I honestly think part of the issue in Pa is everyone who live in the East portion of the state generally goes to NJ Beaches for Vacation (or NY or NC LOL) and people in western portion of the state either go Ohio or NY for vacation. It doesn't seem like people who live in Pa ever travel to either side of the state for whatever reason.
My entire family lived in Eastern Pa off the boat in 1900's as coal miners, I graduated college from State college, worked both in Pittsburgh and Philly, so I consider myself somewhat familiar with the state, and only my own experiences. That said, knew NOTHING about Cedar Point (Ohio) or the lake Erie region until I moved to Western Pa, so I was just as bad. Took my one boy to the finger lake region in NY from NC, and for as much as I thought I knew where everything was at in Pa, it was the first time I ever drove through the Wellsboro area.
What's funny is I had to look because I would have bet NC's population is greater than PA's, but I was wrong.