The wee end of the deal

Why can't little boys pee and then poop? I was changing a very recently poohed in diaper a few minutes ago. I was concentrating on the pooh end, paying no attention to the wee end, when I hear liquid hitting my pillow and splashing on my leg. I quickly cover the wee end of things with a baby wipe and then the pooh end starts going again! I get him cleaned up (and hell I was lucky with that diaper because he hadn't done the pooh in a few days so earlier I gave him prune juice) and that's when I see just how much damage the wee end really did. He peed on the wall, me, my pillow, my bed and worst of all... in my pop. The only thing he didn't do during that change was puke.