Yes, you're right. But if you lose your USB stick or USB stick spoil, your coins are gone forever. So better has several copy of your wallet, in several media, e.g: USB stick, CD-ROM etc.
Is this too simple? What am I missing here?
Why cant you just send your bitcoins to your wallet on your computer. Backup the wallet.dat to a usb stick. Close the bitcoin wallet. Delete the wallet.dat from your computer. Restart bitcoin wallet so it creates a new fresh wallet with no bitcoins. Unplug USB containing your bitcoins.
Doesn't this make your bitcoins completely inaccessible to everyone except the person holding the usb drive?