First, it's as you say an anology, which by definition means it's not the same thing, only that it shares an aspect of the other.
You see the waiter is like the integrator. You pay them x dollars for y food. They don't make the food or pay for the ingredients, they are the channel. They give the x dollars to the restaurant and then recieve a profit based on the bill.
On Monday you go to the Delicious Diner and are served a Hamburger and pay $5 and tip the server $1.
On Tuesday you go to the Expensive Eatery for an equally enjoyable and equally well served Hamburger and pay $20 and tip the server $4.
Why do we do this without even thinking? Because we tip on the bill, not on the food.
In the same way you don't tip $4 on a $5 hamburger, customers don't like 'tipping' the integrator 300%.
So in the case where the customer knows, then they care. And regardless of whether they know exactly, they have a better feel of what the cost is, just because of Costco kits and such.
So their expectation of what the cost actually is drops everyday, but their expectation of a fair margin does not increase to offset it.
Next time you go out to eat someplace new, decide on your tip before the bill comes, just based on the value of the meal/service you get. Why not?