I think you're ignoring the official "atta boy" that goes along with the card. They hand in these cards to their supervisors to get credit. It's proof positive the employee is doing a great job and is appreciated by their clients.

That being said, I wrap the card in cash when I give it. ;-) The only exception would be at the front desk. If they are very accommodating, I just thank them and give the card. It feels like an uncomfortable quid pro quo to wrap it in cash when dealing with the front desk.