My own 2 year old often doesn't pee until 1.5 -2 hours after she gets up. I think it's a control thing with her. It secretly drives me a little batty, but I try not to show it.
On the other hand, it's not an option here to leave the house without trying to pee. So it's possible these parents just don't want to fight with their kids before leaving for daycare... It's not what I would do, but I guess I could see how it happens.