Google is your friend.
Reporting the face value of the coins has been tried, and the IRS really tried to put the hammer down on it.
Last I heard the good guys were winning, but I'd hate to have to defend myself (even successfully) against the IRS. I just don't have that much money or time, and they know where I live.
As to "why" they still have those numbers on them, I believe the reason is because the laws defining what the gold/silver content of a "dollar" is were never really repealed. One oz of silver is still "one dollar", as it were, it's just not equal to a "one dollar FRN note".