bitcoins are stealable. The thief just has to steal your harddrive.
I can use an encrypted file system.
Or I can encrypt my wallet.dat file when I'm not using the bitcoin software.
Or I can have most of my bitcoins encrypted on a distant machine, and use only small change for my local machine.
And so on...
A sufficiently smart thief will social engineer you, or just steal jewelries and other stuff from much easier security system.