KLM almost certainly has hundreds of passengers a day whose gross margin is in the pennies.

True, but Google has Billions of customers per day whose margin is in the pennies, and a few hundred thousand significant account holders.

An account holder chosen at random is most likely to be in the former category, unlike klm where a customer chosen at random is likely to have a much higher margin worthy of a few dollars of support costs.

Some might argue a company should support a customer well even if doing so puts that customer as a lifetime lossmaker though.

They don't have billions of Adsense users, hence the comparison with KLM. And even a small publisher can grow into something big.