To me, referring to a "middle" when the distribution looks like this is not very useful: https://en.wikipedia.org/wiki/File:Distribution_of_Annual_Ho...
Is the median $55k household in the US reasonably comfortable, able to have a family and buy a home without frequent financial stress over expenses like buying groceries, filling up the tank, or paying the water bill? If it's true that most Americans could not quickly produce $2000 in an emergency, I find that hard to believe. $55k DINKs are doing okay, but add a couple babies to the mix (not unreasonable for a "solidly middle class" family), and I think you're in for a rough time if you're saving for college and retirement like you ought.
http://www.denverpost.com/opinion/ci_22490345/kline-americas...