Basically agree with what everyone is saying, it doesn't matter to the market if some coins are lost.  But, I'd like to point out that we probably don't have to worry about a "majority" or bitcoins being lost.  People are going to be careful with things that are valuable, and take extra precautions.  Of course accidents will happen and some wallets will get destroyed, etc, but not to the extent that it will ever be noticeable in the grand scheme of btc currency.

If I had a wallet with hundreds (or more) BTC on it, no back up, and the hard drive crashed, you bet I would be paying one of those overprice hard-driver recovery services to extract the wallet.dat for me.  "No, I don't need the irreplaceable family photos, just get me my bitcoins!"