I just read this thread again, twice, to make sure I understood where you went wrong. This post is the key:
You can get a good idea of how many are in circulation, but as time progresses, you will have less certainty of how many are saved vs. lost.
Let's assume it's the future and all 21 million have been minted. Let's assume that we see 14 million in active circulation and 7 million that aren't circulating. Are they lost or being saved? Valuations will be less accurate over time. I don't see how they cannot be. Imagine valuations based on the assumption that they are mostly lost, and then have them dumped on the market from a dormant account.
Over time, there is a guarantee that bitcoins will be lost, but there will be no real way to measure the average loss over time. Requiring a heartbeat eliminates that problem and allows valuations to be more certain over time.
More importantly, and perhaps most importantly, the accuracy of valuations over time based on circulation will be relatively constant.
Your entire argument is based on the notion that someone could calculate in advance the value of a bitcoin by dividing
something by the number of coins available. This notion is false; value is what the market will pay you.
The market performs price discovery, and it uses only participating coins to do so. Coins that are not participating, whether they are lost or saved, do not factor into prices at all. The uncertainty over the amount of coins remaining in the system has no particular effect on values.
If the value of bitcoins increases on the market, a feedback system will draw coins out of hiding to reach a new equilibrium. If they decrease, feedback will push them back into savings. This equilibrium will be somewhat higher or lower depending on how many coins are actually lost, but this does not indicate uncertainty of value, and it will not destabilize the system. This change in equilibrium actually represents a transfer of the value of the lost coins into all of the remaining coins.
Oh, and read
this, particularly question 6 and the reply.