I'm in the same predicament right now, while planning ahead for my own maintenance schedule.
The owner's manual for my QX states repeatedly that the 7 speed transmission is maintenance free, not even requiring fluid changes. The local Infiniti dealer advises a drain and fill @ 60,000 miles. So I emailed Infiniti, and they replied back that indeed, the 7 speed auto doesn't need any servicing, but that authorized dealers recommend proper diagnosis and repairs. I emailed Infiniti back asking them what they consider to be "lifetime" in regards to their transmission (asked for both expected years and mileage expectations). I have not gotten a reply yet, but its been less than 24 hours at this point.
Having said that, most of the guys over on the Infiniti forum seem to be replacing their transmission fluid at ~50,000 miles or so... and use the familiar argument that lifetime simply implies the lifetime of the power train warranty.
The transmission on a QX is about double the cost of one for the CX5, so I want to treat mine in the most responsible manner, but seem to be getting the all too familiar positions of both sides of the discussion.