Central banks never cash out majority of their gold holdings. It will be so stupid to exchange hard assets for some fiat paper that they can print any time
Satoshi isn't a central bank though and cannot print his money, though at one point he may wish to actually use his coins and pay or buy something substantial. Maybe a mansion? And I think most mansion-owners don't accept bitcoins as far as I'm aware (though hopefully they will in the future).
Satoshi's achievement is much larger than any central bank, those banks can only control their own currency through a debt scam
This kind of post shows the author lacks financial experience. Rich people don't need cash, but rather accumulating assets (In fact that's what banks are doing every day). But physical assets always have a risk of being heavily taxed or confiscated. Since bitcoin is the most liquid form of digital assets, satoshi need very small amount of other assets, if any.
http://www.arcticstartup.com/2014/09/01/estonian-bitcoin-castleBut what can you do with such a mansion?
And, I guess he already spent large amount of coins, just not those 1 million coins, which might be lost (Otherwise they will be consolidated into one or several wallets, not spreading among thousands of wallets)