Jeep marketing has been confusing customers, I think.... but its marketing.

At the risk of oversimplification,

The transmission has three planetary gear sets (each gives you two ratios), giving the transmission programmers 8 possible gear rations to select from by engaging a combination of gear sets (applying a clutch such that the ring gear is locked). So the transmission is actually an 8 speed. In a series planetary gear box, the gear ratios just multiply up.

However, due to size constraints, the engineers could not make all 8 speed useful (the combination making a unique ratio). So, in the end, there are only 6 useful gear ratios available. In order to get 8 useful gear ratios out of a 3 gear set transmission, engineers needed a planetary gear set too large of a diameter to fit in a case that also fits the numerous applications (without redesigning all the cars).

In 2012 the transmission is programmed to use all six useful ratios when upshifting and down shifting. (although marketing may want them to use all 8 so they have an 8 speed to sell

)

Other manufactures either have more room (trucks) or solved the planetary gearset size problem by adding a fourth gear set (or more). A four gearset transmission gives you 16 possible gear ratios, but I'm not sure how many would be useful (unique). Its a math thing.