They do this with alot of vehicles for different reasons.

The SRT-4 crowd used to complain about running rich at WOT, and at the time I was acquainted with the development folks so I asked what the deal was.

On that specific car, I was told it was done for lifespan of the catalytic converter, leaner produced more heat than it could tolerate over the whole warranty lifespan.
Converters being real expensive to replace, even in 2006, but today would of course be worse.
They have to be really careful about that aspect of things.

It could be something similar or another combination of factors requiring the rich a/f, but believe me the guys calibrating that stuff aren't doing it out of ignorance.

PS this isn't top secret info as the same folks I asked were also on the srt forums of the day, providing the same answer.