The difference is in the input. You pay a fee for every byte in the input data. Zero bytes are cheaper.
First tx has a zero byte
From Yellow paper Appendix G "Fee Schedule"
Gtxdatazero, 4, Paid for every ...
Infura is a public hosted node. It has no way to unlock your local accounts. Even if there was a way, it would be a security risk because anyone can connect to the same node and transfer your funds.
In order to send a transaction over Infura you will need to sign the transaction locally using web3.eth.sendRawTransaction(). The following example is from the ...