Hi Shinobi,
You are seeing things correctly. Theft is possible, and recovery of what is stolen is if not impossible, infeasible. You should think of bitcoins like cash. There is nothing to unwind when someone steals your cash, no recourse -- you either find the thief and make him pay back or be punished in the judicial system, or nothing. Similarly, just as with cash, stealing is possible if someone can come into relatively intimate contact with your stuff -- the fact that your stuff is digital and the trespass over a network (most likely -- though physical theft of a computer system is also possible) plays merely to the ease or difficulty of the thing -- not to the nature.
So, let's talk briefly about security of assets. To prevent theft and to allow recovery, it is possible to store your bitcoin wallet on a secure encrypted drive that would be, if not impossible, infeasible to access without your consent. You can back up the encrypted volume and rest relatively sure that if your main disk crashes, you can restore from the backup. Really, again, just as with cash -- don't store it by the fireplace, keep some of it in a vault, and you'll be more or less OK. Your comments about the clearing house and how it relates to theft don't really add up -- I think you don't yet understand how the bitcoin system works. You want to go read the FAQ and focus on the notion of the blockchain, how it works, and how it is secured by the distributed bitcoin system. It took me a few hours of reading and pondering, but now I get it.
Your suggestion that a great amount of bitcoin wealth could be destroyed in one go is again possible, but just as with any currency, unlikely. It's *possible* that Bill Gates' foundations would all bet all of their money on one go of a Vegas roulette wheel, or that they would store all of their assets in bonds and locate them all in one building that could go up in flames. But this is very unlikely. If someone had enough bitcoin wealth that their assets made up a large part of the total asset base, it's highly likely they would distribute the wealth among several wallets, and across multiple computers and locations. Again, just as with any kind of money, a psychotic anti-self-interested party could purposely spend tons of money simply to destroy wealth (buy a billion dollar bills and burn them all, say). Bitcoin fares no better, but no worse, in these cases. (If anything, it fares better, because the loss of the digital assets could be replaced simply by allowing the bitcoin blockchain reward to last longer than it currently does, or similarly, to allow more decimal places in the bitcoin unit count.)
As far as the relative liquidity of the currency goes, you should think of it as a digital medium of barter, and like the older style bartered goods, it comes with a level of inconvenience at the moment. This is a function of the small size of this nascent market (if the market were large enough, you wouldn't worry about exchange, but rather, buying things with your coins, which is itself quite easy) and of the growing pains in dealing with the transfer of funds back and forth into a "risky," "hacker culture" medium like bitcoin (seen through the eyes of, say, PayPal).
This isn't a complete answer, but I hope it helps.
-KS