"All else being equal" is a huge assumption. Will your company offer the same environment, flexibility, openness, remote work? You should first assume that Buffer keeps their employees very happy to be able to openly publish their salaries.
That's great, but what if Niel has a kid? Suddenly priorities are shuffled in a big way. Maybe he needs a 5% raise to afford <whatever it is that the kid needs>? Is it worth it to the company to lose the employee over 5% of salary?
I think the point of the transparency is that they'd discuss a situation like this as a company.