The total amount of Wallets holding at least 1 bitcoin is under 250,000.
How do you know how many wallets have 1 BTC?
How can you tell which wallets have which addresses in them?
According to that article on wired.com there are 246,377 Bitcoin Addresses with 1 Bitcoin in them at the time of it's writing and don't forget that most users have more than 1 Bitcoin Wallet(I have 9 for example).
I'm assuming they made a script to check every wallet's balances.
That's 246,377
ADDRESSES, not
WALLETS. Most wallets have multiple addresses ( I have some wallets with dozens of addresses ). Many people also have multiple wallets ( I have a few blockchain.info wallets, a few dozen Bitcoin-Qt wallets, an Armory wallet, an android Bitcoin Wallet, and several paper wallets, each with their own purpose). Many of those wallets (and addresses) are empty at the moment, but they've all held bitcoins at one time or another.
I generate a new address for almost every transaction. It would be very difficult for someone to figure out how many wallets, or how many addresses I control just by looking at the blockchain.
