This is actually one of the strangest things about it tbh. How can there be over 1 million unsold early adopter bitcoins? They can't all be lost and the people who held on to them through the $250 peak have some serious self-restraint
Why is this strange?
The early clients did mining by default in the background, and per-block difficulty was very slow.
It does not take very many people playing with it for a few weeks and throwing away wallets to get to 1 million lost bitcoins
I read on bitcointalk.org (so take with a grain of salt) that a new wallet was used for the initial blocks, so there are 50 coins in each of ~40k wallets.
It's entirely possible that early on they used throw away wallets while testing and the alleged $100m in "early coins" are all inaccessible.