Vanguard's MM accounts pay more, without the FDIC guarantee.
I would argue that's a positive trait, not a negative. FDIC gives you government insurance on your money up to $250,000 if the institution failed.
The Vanguard Federal Money Market is invested in short term government securities, the same treasuries you are a fan of. That means the investments are backed by the government regardless of dollar amount.
Aren't most Money Markets not technically insured though?
Money market savings accounts, like those offered by banks including Capital One 360's, are FDIC insured.
Money Market
Mutual funds, like Vanguard's, are not FDIC insured and fall into 2 groups.
Federal Money Markets invest in short term government debt. While they lack FDIC, they are still backed by the government since they are invested in Government debt.
Other money market mutual funds, like Prime and Municipal money market mutual funds, are not FDIC insured and they are not invested in U.S. Federal government debt, so they don't have the same level of protection.