A driver only makes sense for rich people who live in a big urban area like Manhattan where it's probably cheaper long term to hire a guy to drive your car than pay for parking.
I'm sure their decisions needn't 'make sense' in the way that you mean. Anything they could spend on their personal misbehavior would pale by comparison to their massive privilege-incomes. Of course one has a driver, simply because driving is a chore.
For a lot of the rich - for example I once lived in a town that had Waltons in it - armed, trained drivers and a 'plainclothes' following car, both cars with security men, are necessary if they want to feel safer from
justified retribution kidnapping. I do believe there are even rich people with 'dummy limos' - who emulate the official practice of making transit a 'shell game' (which one is he in?)
I think you guys aren't crediting how small such expenses are compared to the privilege of this class in 2012.