530XI or M35X and why?

I remember seeing a vid on the net of a AWD 5 series paired up agains an A6 quattro, both on rollers. the showed that the BMW was abled to get off of the rollers while the Audi stayed on. I cant remember where I saw it but it was pretty cool. Someone explained to me why it was that the BMW was able to get off but I cant remember. Anyone Know what Im talking about? I personaly would go with the Infiniti. Better value IMO