The way I see it, you have to wash your hands throughout the day. If you don't they'll become dirty, so I will wash my hands about 3-4 times a day, which I will do at the convenient times of after going to the toilet. I don't really think that the act of taking a piss really dirties your hands up very much provided you don't piss on your hands. So I don't think it's a huge deal when someone doesn't wash their hands after going to the bathroom, but I always do just as a force of habit.
When I was younger, I worked at a warehouse during my first two years of college. Anyway, this dude was wearing shorts, shit on himself in the break room. It ran down his legs and all over the break room floor. The dude panics and tries to clean it up with paper towels which does nothing but smear the shit every where. The guy just grabs his stuff, wipes his face with his unwashed hands, and asks to leave.
The guy eventually quite because everyone started calling him Mr. Poo Poo pants.