It comes down to each person's anti-virus installed on their PC. Norton, MSE, and McAffee for instance use a pooled database of known problematic sites to block. If one company says this could be a potentially harmful site, they toss it up there in the database.
Anti-viruses like Kaspersky use their own heuristic analysis to determine in REAL-TIME if something is a threat or not and analyze flash, JavaScript, and malicious code on the page (which is a lot better and blocking threats) instead of relying on a standard database which may or may not be current.
I have been told before that that page pops up as having a virus, but it is just the JavaScript that takes control of the browser. It probably hasn't been removed yet from that database for the Anti-viruses on those people's computers.
