Does this "$1B in revenue" include the $ that customers have deposited in order to buy cryptocurrency?
They would only record revenue when they charge a transaction fee, or any other charge/income that can't be used by/returned to the customer at their discretion. Revenue is only revenue if it doesn't incur a matching liability.
Coinbase is a counter-party in all trades e.g., people buy FROM Coinbase or sell TO Coinbase. So $1B revenue number would include all deposits.
GDAX accounting would only count commissions as revenue.