The reason that people who lost money in Mt Gox can't get their money back isn't because it was in Bitcoin.
Your point is sound (deposit insurance is different from who or what issues a currency), but in practice that distinction doesn't help anyone looking to replace their wealth storage in dollars with something else. The reason Mt Gox isn't an FDIC insured bank is because their deposits are in bitcoin, and FDIC doesn't insure anything that isn't in dollars.
I seriously doubt the US government will start insuring bitcoin deposits because 1) it doesn't control the currency, and 2) because it wants to encourage people to use dollars, not bitcoin. Lack of FDIC insurance on bitcoin is a (major) downside to using bitcoin as a wealth storage replacement.
Note that I'm talking about wealth storage, not short-term transactions. Transactions can be done in whatever currency the two parties agree upon (dollars, bitcoin, Ferraris, head of cattle, whatever). That's been possible since the dawn of trading between two parties and bitcoin is perhaps useful there.