A lot of people who compete pull with a neutral and solid spine. If you watch that super training TV video posted a while back all those guys are pulling with a solid spine. On Eason's video his lumbar is curved as hell before he even touches the bar, and when he starts his pull it's the first thing that moves up / breaks.
You can even rewatch it for yourself.
You can see that a lot of top guys pull with a curved back.
Also, you need to take into consideration how thick these guy's erectors, so a lot of back rounding is masked.
I've noticed as my erectors have gotten thicker it only looks like I'm rounding back back less when in fact I'm pulling the exact same way I have pulled to get my erectors to the size they've gotten.