So the question is.... did they think it was worth the risk of getting caught? Or did they expect to get caught and think that cheating would still be worth it even if they did?
Anytime you cheat, you know there is a possibility of being caught. Nvidia new the possibility was there. They also know that with their popularity they will still have many supporters no matter what they get caught cheating at. Just look around at the number of people rushing to defend them for this. The number one excuse I see is "it's just 3dmark". Unfortunately I feel a lot of those same people will still defend them even if it gets shown they cheat in game benchmarks too.
It's all a matter of them weighing the options and picking the choice they see most fit. I personally think they made the wrong choice, but only time will tell.