IMO this happens with a LOT of standard advice regarding startups. The problem is that there are as many ways to do a startup as there are founders and its too tempting for VC's to infer 'wisdom' from their immediate samples.
I suspect that this happens because as an observer its extremely hard to distinguish causation from correlation. Also, it seems that VC's tend to view 'emergent' success in terms of their own work ethics.
Sam's not the only one though. Paul Graham did this too with his two founder rule for startups.