Buying property, you are betting on the politics, economy, security, and many other things on the location of your property. You have to worry about the earthquake, fire, flood, storm, hurricane, or typhoon.
Same with Bitcoin, e.g. most people suggest this big boom is linked to China (politics) and when there's a security breach, or a big arrest (like mt gox fueled crashes in the past, or SR arrest) the price goes down.
Buying stock, you are betting on the market, competitors, the leadership of the CEO, and many others. Moreover, you have to worry about insider-trading and fraud in accounting.
Same with Bitcoin, you're betting there's going to be a market for oyu to sell your coins to, you're betting your competitors don't do a huge dump before you do. The fraud an insider trading is even more of a risk with Bitcoin (look at how many exchange have disappeared, look at Fontas on BTC-e)
Buying gold or silver, you have to find a safe place to store them and then you need to find a safe place to sell if you want cash.
Same with Bitcoin, you have to find a safe exchange, preferably in a stable region with good political ties to whatever country your in. Then you have to get your bank to be okay with you transferring in a massive chunk of fiat from Bitcoin (I know some banks in hte UK wouldn't be comfy with that)
I believe now you will agree with me why I said investing on BTC is the safest and the easiest.
That said, I'm not saying it is risk-free. It is highly risky, but investing on anything is risky, and holding fiat without investing is even more risky.

Betting in a regulated controlled market is far safer than Bitcoin. As someone pointed out, there's nothing stopping allt he various middlemen here running with your money. In a lot of cases, you've not got a leg to stand on with regards to legal recourse in the Bitcoin world. Don't kid yourself, Bitcoin is just as, if not more risky than other proven tried and tested investment options.