2 brothers, Joe and Bob get equal dollar amounts of securities as a gift. Joe immediately sells his securities and deposits the money to a bank account. On the other hand, Bob keeps his securities positions and holds them in a brokerage account. After 5 years, Joe has $10,000 in his bank account, while Bob has $30,000 in his brokerage account. The $20,000 difference between the account balances is explained by: