Why?

Good point! And jewelry makers, and "holers"!

I suppose the laws are separate because paper notes are instruments of credit, while coinage is specie. If you got a silver dollar in change, that silver was yours, to do with what you will. Spend it, melt it down, have your baby teethe on it (once a common non-monetary use of silver dollars). Or drill out the date to try to keep it in your slot machines and out of collectors' cabinets. Just so long as you didn't alter with intent to deceive; a hobo nickel is perfectly lawful, but not a racketeer nickel! One thing occurs to me, though; once the rising price of silver brought on the clad coinage (and, later, that of copper begat the Zincoln), didn't that make coins less like specie, and more like instruments of credit? Couldn't you argue that holing a 1964 quarter is within your rights, but violating a 1965 could run you afoul of Title 18?