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...
You can. You can do similar things with gold, paper money, and so forth. The fact that you can make it difficult to steal doesn't mean it is inherently any more theftproof than anything else.