I agree. I grew up in Ohio, and to me, Pittsburgh and the rest of western PA is part of the Midwest. It has the same farmland/steel-town culture that Ohio does.
Obviously Philadelphia is not, so I would argue that the dividing line is somewhere in the middle of the state.
Well, see, this kind of depends on your definition of "Midwest". I grew up a fair distance west of Denver, and to me, the dividing line between East and Midwest is Chicago. The "real" west begins at Denver. This neatly divides the country into approximately thirds.
But to say that Ohio and western PA are "Midwest" because they're west of the Appalachians... bah. You easterners need to get out more. And if you think steel town culture makes you part of the Midwest, well... come west of Chicago and look around. You don't see many steel towns out here.
I mean, I suppose that's the labels that you grew up on, and it's how the locals label themselves, so on that level it's hard to argue with. But anything that includes "West" as part of the name (or even "Mid") that includes Pittsburgh... look at a map of the country, and then explain to me how that makes any sense at all.
Obviously Philadelphia is not, so I would argue that the dividing line is somewhere in the middle of the state.