Because bitcoin and other cryptocurrencies are seen as property by the U.S. government, capital-gains taxes apply to every transaction made. Even if you were just buying a cup of coffee with bitcoin you have to report every transaction using bitcoin. Each sale or purchase technically constitutes two transactions: (1.) selling property (bitcoin) and (2.) using the proceeds of that bitcoin sale to buy a product. So the person who bought a $1 million home using any cryptocurrency would have to pay capital-gains tax on the transaction as well as real-estate taxes.