Interesting. Maybe it's running that rich in order to lower the EGT's a bit and keep the cats alive a little longer, since the Republik of Kalifornia now requires all emissions equipment to last for a minimum of 120,000 miles.
Supposedly, that's what happened to the RX-8s - a portside ECU reflash severely richened the part-throttle mixture to help keep the cats alive. The unfortunate side effect was horrible gas mileage and a few missing ponies, both of which probably cost Mazda more in terms of money and marketing than a few pre-120k cat failures would have 6 year from now.