Does anyone have any idea as to why Apple only released one of these models instead up just updating the whole MacBook Pro lineup to this new form factor and retina display? Does it have anything to do with price discrimination in order to get the most money out of it or did they actually have a reason for only releasing it in one 15" model?
Yes.
It's because this is a product that's meant to set the stage for a transition. Transitioning away from not having optical drives, no ethernet port, thinner profile. And the screen is new so it's expensive.
Apple wants the prices to drop for the screen production, so they can replace their existing lineup, not augment it. Maintaining a product-line that has two symmetric sets of Mac book pros (2 13" models and 2 15" models) is more expensive and in-efficient for Apple's focus and desire for having quickly moving inventory. The more variations you have of a product the more complex and greater the in-efficiencies.
This laptop allows a platform and runway for the software to catchup to retina screens and for ethernet and optical to have time to become even more irrelevant. In about 1-2 years apple will discontinue the thicker MacBooks and replace the line completely with the new thinner model at a better price point.