I agree that it's not a 'currency killer' in the short run BUT if we speculate that BTC reaches mainstream popularity and a total market value in the 100-1000s of BILLION USD the fact that an 'unknown' amount is in circulation makes for a very strange variable.

All of a sudden my old 1BTC wallet on my crashed laptop hard drive may be worth 100s of days of mining network wide, and even the speculation that a 'previously unknown' wallet containing 100BTC (there are a LOT of those sitting on old phones and hard drives already I promise) would have possibly disastrous effect on currency value etc.

All I am saying is that there are a LOT of factors to consider and BTC loss over time is a major one.

My argument being: A finite supply of a currency is one of the factors people REALLY need to think about when it comes to BTC. And I guess I am saying that it's a real problem vs. a currency with increasing difficulty and a non-finite supply.