I think they store bitcoins just like everyone else store them because bitcoin wallets are guaranteed not to be hacked,
Uh.. Saying "Bitcoin wallet" could even mean web wallets, which are definitely not hack-proof.
maybe they store keys in software not store them on internet connected devices.
..or maybe offline non-digital backups like a piece of paper so no hacker can reach it? You know, like people always recommend newbies do.
like the satoshi wallet until now it is still safe no one can hack the satoshi wallet.
Satoshi's wallet is uncompromised because safe to assume that he knows what he's doing security-wise. Probably only less than 1% of people are capable of such digital security.