It's component deterioration from age that really gets you on a luxury car. Seat motors fail, wiring harnesses deteriorate, etc.
It's also worth mentioning that they didn't crash one. With enough road hours eventually it will happen. The vehicles that can be serviced by a normal shop will be cheaper to repair.
The lack of downtime is very impressive but if it's really that much cheaper than running a fleet of town cars then why do they need to twist the numbers?