
Wouldn't that be confusing for you? (It would for me)
Assuming you want the whole tr so you can style it out of existence. Every once in a while, the thread nesting would get wacky--it'd be harder to track nesting depth. Not to mention replies to a non-existent post would start to look silly.
I'm gonna go build my own theme park! With Blackjack! And hookers! In fact, forget the park!