Correct. I wager that plenty of people were toying with Bitoins at some point but shrugged it off and deleted (or lost) their wallet for one reason or another (see the story of the guy who lost 7500 BTC). Wallet gone, coins are gone, forever.
My encrypted wallet is backed up periodically so that a hard disk crash won't wipe me out. If Mt.Gox goes evil, a lot of people will lose their cash/coins, myself included, but Mt. Gox makes a pretty chunk on every (frequent) trade, so they stand to gain a lot more from being cool than being evil, which serves everyone.
Bottom line is that Bitcoin is an extremely interesting technical experiment, but more of a gamble than a secured investment. It could all go sour in a minute, or turn into a mind-boggling foundation of a world economy, but fools are parted with their bitcoins on a regular basis, as the story shows.
Don't hand over your wallet to some guy at the street corner, I'm just sayin'