I have never cleaned my deck either. Every once in a while, a plate of dry grass falls off and gets whacked by the blades. I figure so long as I don't scratch up the paint on the bottom, it should never rust. And if it does, it is pretty heavy gauge, so it should take a long time to go through!
I have never washed my tractor either. I am afraid that water on the deck would just funnel in to the bearings.
I do change the oil and I did the 50 hr service. I do grease the deck a few times a season... And I agree it is MUCH easier with the deck off.