First of all, there's nothing that causes fiat money to inherently lose value over time. It's a matter of the policies imposed by the government, which are enforceable thanks to the simple fact that by the end of the day, the government can take your stuff or put you in prison if you don't play by the rules.

By the same token, the government has the power to regulate gold or Bitcoin if it chooses to - including taxing or confiscating it. There have been many instances of governments confiscating gold or making it illegal as an instrument of trade. The consequences of defying such orders can be dire.

But that aside, I think that the parallels you're drawing are strenuous. One is a virtual currency fully dependent on modern technology, the other is a commodity that cannot be destroyed due to computer failures, hacking, or protocol design flaws. One critically depends on enough people staying interested (to process transactions), the other doesn't. One has a public ledger of transactions (with all its privacy implications), the other has perfect privacy. One has no intrinsic value, the other has some bottom-line value dictated by industrial demand and its lasting appeal in jewelry. One is a relatively new development without demonstrated long-term viability, the other has been around for millennia. One has definite and painful depletion mechanisms built in (which some believe may hinder future trade), the other... well, we're many generations away from hitting a wall.