There's a significant difference between Bitcoin and cash, which is that the worst-case scenario for loss of your cash is the government in control of it just prints more and gives it to you (in effect, distributing the cost of your loss among everyone who holds that currency). This is not technically possible with Bitcoin, and AFAIK no system has grown up organically yet to provide some kind of "loss insurance" in the form of keeping some BTC in reserve for making victims whole.