Because the CSD says to you 'there are four Permiers in the cabin tonight' with a look of shock. Although only two of them were taken away in a private car; the other two took the bus!
Proof that even within a tier, there are still subtle distinctions!
I've seen a couple of Prems who frankly haven't behaved any differently to normal pax. Most of the people I see getting the full on car treatment are diplomats/government ministers.