I've been thinking about this, too. You are so right. I really wish ABD would stop the whole tipping of guides thing and just pay them a decent wage and/or charge me more at the outset so I don't have to worry about it.I've actually been thinking about this in the context of group size. One thing about ABD really trending towards the larger group size is that the guides then make more money, so it I imagine the guides prefer the larger group size. The whole tipping issue with ABD definitely does not work to align interests for everyone.
One of the wonderful things about Japan was the no tipping anywhere--except for our adventure guides we were reminded, LOL. Sometimes restaurants added service charge, but that was actually fairly rare. It was so so nice. I wish it was like that in the US. In Japan, tipping is considered rude and an insult on a couple of different levels. Basically you are insinuating that they don't make enough money, and/or that their employer doesn't pay them fairly.