LOL, I understand this, but I mean that if a lot of these people who are presumed "incapable" of a large pull would pour the same effort and focus into their training that you have for the past several years, I surmise that they wouldn't look so incapable. Just as you said...
How many people who are really, honest-to-goodness trying to achieve a big deadlift fail to get beyond four plates?
The thread title and initial question asked if it was possible for most people. If someone does not pull 600 because they were never trying for it in the first place, or they weren't willing to put in the necessary time and effort, that misses the entire point. Brick's contention seems to be that (some) of those people are incapable of a 600 pull regardless of whether they put in the time and effort to reach their potential; those of us on the other side believe that most people who actually did put in the time and effort to reach their potential would find that a 600 pull was reachable if that was a primary goal.
I also chuckle a bit at @on_edge's story above. If a 6'1" 180 pound 52-year-old who doesn't really focus on powerlifting or limit strength pulls over 400, is it really far-fetched to believe that 20 years ago, in his physical prime while spending a couple years dedicated to a big pull, 600 would have been impossible?
I think there's one other sorta-misperception floating around here, this idea that saying a 600 pull is possible for everyone somehow diminishes the feat. On the contrary, I think it elevates the feat, because it suggests that those who achieve it are among a select few that actually did channel the necessary combination of time and effort to get there!