Well, I should not use the word "reward", should I? The Pattersons don't believe in rewarding their children when they do something good because nothing the children do can be allowed to please them. What I should say is that the level of punishment is directly pegged to how pissed off John and Elly happen to be at any given moment. What really seems to infuriate John and Elly is any sign that the children are showing 'ingratitude'. Given that the two of them are incredibly selfish people who want a medal and a parade for the performance of a moral obligation, 'ingratitude' is best defined as any behavior that might imply that John and Elly's whims are not the only thing on Earth that have any value.
This sort of hatred of 'ingratitude' helps explain why John and Elly are always angry. Simply put, they think that their children are trying to mess with them because they hate them and want to destroy them. This, in their mind, justifies their making children live in a constant state of apprehension so that they don't get any funny ideas about how Mommy and Daddy are what Chris Rock calls "low-expectation-having motherfuckers."
The end result of this horrible emotional abuse is to produce children who lie as a matter of course. They really can't help it and aren't doing it to be evil. They need to lie to protect themselves from insane, hateful parents who blow up over trivialities and try to elicit the praise said vermin selfishly withhold so as to conserve gratitude. Also, they become hyper-vigilant to the idea of being attacked. My guess is that if Mike weren't habituated to the idea that John would just saunter on over and start yelling at him because he had a hard day being reminded that he's not a big deal, he wouldn't have squealed about how Rhetta and Martha betrayed him.
Fortunately for him, though, he has a penis and thus gets fawned over because he can perpetuate the family name. Liz and April have to choose the safe option.