To each their own, I suppose. If you enjoy living in Pittsburgh, knock yourself out. But 'most livable'?
Pittsburghers don't live. They 'pretend'. As long as we've got 'one of those, too' we're perfectly content. Tapas bars all the rage in other cities? The Pittsburgh response is 'yeah, we got one of those'. You have a booming theater scene that feeds into the national dialogue? 'Yeah, we got a couple theaters, too.' (Have you ever heard of anything originating at the Public and going national? Unless it's a play about--of course--Art Rooney.)
This idea that somehow cheap housing is Pittsburgh's trump card is a crock. You get what you pay for. Take, for example, San Francisco. Real estate is expensive. But you also get--for free--spectacular views, clean air, year-round livability, access to the Wine Country, national parks and the joie de vivre of a city that celebrates diversity and tolerance and whimsy. In Pittsburgh, real estate is comparatively inexpensive. And for that you get a few miles of accessibility along a couple of dirty inland rivers, fewer sunny days than Seattle, an intolerant, grumpy, racist population and risk averters. And God forbid if you don't make the Steelers the focal point of your life.
One of the damning qualities of Pittsburgh is the inability to hold onto the world class students who come through CMU. Compare Pittsburgh's retention rate to Northern California/Stanford, Boston/MIT, Boston/Harvard, Duke/North Carolina and other major universities.
Again, what is the standard of livability? A city where people can afford big houses and large lawns and cut themselves off from the world outside of their neighborhood? A place with a large reserve of museums and symphony halls funded by the remaining fortunes of the barons who polluted Pittsburgh and then took their treasures to other cities? (It's telling that one of our major 'cultural jewels is dedicated to a man who was run out of town, hated Pittsburgh and never returned after he left.)
Should we really be trumpeting an impressive health care system that thrives here because of the ripe pickings of an old, obese, sedentary population? That's great if you're planning to have a stroke. But take me to Denver, where the health care system might not be as good since people have less need for it.
Honestly, do you really think that the residents of comparably-sized markets--Seattle, Denver, Minneapolis, Charlotte, Portland, Baltimore, San Diego, Atlanta--would really trade places with us? Really?
Life is about more than a big living room with a wide screen TV.