After a series of minor design updates, it was completely redesigned on 2008-10-14 and had an SD slot added to most models on 2009-06-08, at the expense of the ExpressCard slot. On that date, the range was also extended “down” to the 13” model, making the Pro moniker synonymous with the unibody aluminum housing again.
On 2012-06-11, around six months after a previous CPU refresh, the Pro range was “re-scoped” to drop the 17” model in favor of a brand-new, ultra-thin 15” model with a Retina display (the range comprised a 13” model, a 15” model and an updated Retina-enabled 15” model)
Whereas the “traditional” models still have room for an optical drive and a number of extra ports:
The new 15” is almost as thin as an Air:
Sadly, that means it lost the battery indicator lights, which are one of my favorite features of the older models.