If you look at many competitive deadlifts, you'll see that the lower back, or lumbar region is still neutral, but there's a rounding of the upper back.
This is innocuous when it occurs, and if the lifter is aware of it, and it also serves to shorten the ROM somewhat.
I think Rippetoe's treatise on proper deadlift form nails it, that can be found in the CFJ section of the website. Thats something we should all strive for even in maximal lifts. However, if you look at the best in the world, this isn't how it goes.
This will occur even when the best form pullers, i.e. Olympic lifters, pull a maximal deadlift. You will see how their form changes from the one optimal for OLs to one similar to the competitive PL form.
It's ludicrious to hold up a 95-135# deadlift as a proper demonstration of form for ALL deadlifts. It doesn't happen that way in real life.
Mike O'Donnell had a great point...some people aren't well suited for a lift.
And, when they talk about "health lift" way back in YE OLDE DAYES OF IRONE LORE, they are talking about a handful of people, most of whom were very well suited for lifting in general who were doing it. The "deadlift" as show in the video isn't "in our genes". That's la goofy statement. What we've done evolutionarily is bend over and pick things up. These things very rarely had handles, or were balanced on each side. We instinctually try to get our hands under it, and to get the object as close to our body as possible. That's the primal movement pattern.
Jesse, It'd be very educational for everyone if you filmed a deadlift workout where you hit a maximal deadlift and toss it up on YouTube. I'm sure that's something everyone would appreciate seeing. I've got some there, and if people want to comment about my shitty form, portruding gut, or frequent use of the word "um", feel free to do so.
And, I'm not saying maintaining form is bad. If you have the trigger that you've reached your max when you lose that form, then that's probably a valuable thing, especially for those with tricky backs, given that you are using the clean grip deadlift as a training movement, and not as a competitive lift. However, that trigger almost always needs to come from an external observer, and not the person performing the lift.