I've eaten pizza in 6 of the top 7 on that list (never been to St. Paul). And my friends in San Diego will be appaulled that San Diego is 7. They come back to the northeast almost exclusively for pizza.
I live right in the middle of the pizza corridor. About an hour from NYC, and about 1.5 from Boston and Providence. And all roads cross on a city that I'm shocked wasn't listed, where I95 meets I91 in CT, the split that takes you from NY to either Boston or Providence, sits New Haven, CT. A beautifull old city on the water, home to Yale University, with cobblestone sidewalks and streets lined with elms. It's also home to two of the most famous pizza joints in the country, Sally's and Pepe's on Wooster Street. Pepe's is the bigger name of the two, and frankly a nicer place, but personally I'm a Sally's guy. We go every year in December for my buddy's birthday. And if you go on a busy night, the lines for both places to get in can get so long they'll cross. And I've seen fights break out over who's better. The city's specialty is the brick oven pizzas, with a crispness to their thin crusts that doesn't really exist in the NY thin crust pizza. They also both specialize in the locally invented white clam pie, which Pepe's claims to have invented.
And as with most of these cities, chefs come in to work at these places then open their own spots in town and you end up with local favorites. Mine is Bar, which brews it's own beer, with 4 selections, and is the coolest of the buildings. But there are others too.
New Haven was in the Pizza Paradise episode on the Travel channell, with NY and Chicago. And recently GQ did a piece on the 101 best pizza spots in America, and there were five (IIRC) in the greater New Haven region.
Whenever I was down in the Burnside area of Portland to see a show, I would almost always walk down to Dante's Pizza between bands and grab a slice. $3.50 gets you a giant slice and they have a window you walk up to and place your order.
Thin crust, extra greasy, large portion.. what else do ya want?