You probably don't get it because I pretty much avoided addressing that part of the question, focusing instead on the US versus the rest of the world.I still don't get it. Are you saying tipping is not a good incentive, or not a good way to show gratitude for good or excellent service?
I'm really not trying to be an a$$ here but I'm completely bewildered by all this to do over showing dive operators a little financial love.
But to address it (sort of), I would say a tip is indeed a good way to show gratitude for good or excellent service. It's just that, under the US custom a tip has become something more than that. In most countries in which tipping is practiced, leaving a few coins on the table or giving someone a small token of your appreciation sends the message without being so in-your-face; it's seen as a token of gratitude, not a substitute for a chunk of the person's monetary compensation for their work.