Not 'free retake', but 'free practice exam'
...with the bonus that if you pass the practice exam, you don't have to do the real thing.
I was talking to a guy at work this morning about the free retake offer from Pearson Vue. I think the best way to think of it is that it gives you a free practice exam. This guy is a sysadmin here day in, day out. So he should know his stuff already. A few skims through the summary pages of a study guide book, and that should be enough preparation for a practice exam. And if he passes it, then great - he doesn't need to do the real one. And if he fails, then he's had the perfect preparation for the real thing.