We do crossells and upsells, affiliates only get paid on upsells to our other sites. This reprents over 20% of our total income if you add the money done upselling and the sales people you're upselling to are sendign you back in exchange. There is no way we could afford to pay 60% to our affiliates if we were not able to make that extra money.
Now we could pay 40% or 45% instead of 60% and refuse any members traffic trades, but who would signup to a cash program paying 40% when others pretend they pay 80% or more (and shave).
Thing is because of competition any cash program pays its affiliates as much as possible, trying to make its margin on volume. Not paying webmasters on crossells is just a way to pay more without shaving.
As for retention, we are the only cash program that publishes its numbers:
http://www.totemcash.com/free/figures.php
My 2cc.