Having private keys or not don't imapct the supply of Bitcoins. In case of web wallets and exchanges, users no doubt only have representative value of bitcoin in their wallet and not real coins but those values aren't manipulative and web wallets or exchanges do have those Bitcoins in their cold or hot storage.
snip~
Again same thing, exchanges do have real Bitcoins with them equivalent to what users have on their representative wallets. There is constant influx/outflux on exchanges which ensures there is symmetrical cash (Bitcoin) flow on system. Which ensures in the case all users withdrawing Bitcoins, exchanges have enough to pay them all.
You've missed the point, which still stands. A lot of people who think they own Bitcoin actually don't at all. Until only you own the private keys to your wallet, you have absolutely no control over what happens to your coins, and no way of ever verifying if the exchange actually has your coins.
Sure, some exchanges can prove some of their actual Bitcoin balances, but in general most cannot reliably prove solvency. You must have not heard of all the problems with major exchanges to believe they have the system fixed.
And the point is, even if they do, you still have to trust that they will honour your Bitcoin withdrawals.
I did mention this yesterday... why I feel mass use and mass adoption is falsely expanded by a lot of newcomers who actually don't own nor use Bitcoin.
