[mitt_romney_12]

The Big 3 distinction isn't based on firm size (McKinsey, Bain, and BCG only have 38k, 25k, and 15k employees respectively) but rather on prestige and type of work done.

[ThisIsTheWay]

Is this distinction why they are often called the Top 3, not the Big 3?

[mitt_romney_12]

I haven't really heard Top 3 so I can't say, usually it's Big 3 or MBB. The Big part refers more to prestige and influence rather than actually size.