How can coinbase charge less than the average transaction fee?
Coinbase holds a large amount of Bitcoins. When you buy Bitcoin on Coinbase, they do not need to actually send it to your wallet, they just need to say on their servers that you own X amount of Bitcoins. They charged you $1.49 because of the payment you used and/or to take a small profit. If you were to move your Bitcoins to a wallet you actually own at home, you would have to pay the miners.