But you're missing the point about the upgradeability.
Yes, when you add everything up, you could've bought a pricier computer, BUT that's assuming you have the total to spend, in your pocket, right now. Obviously, if the buyer can afford a better specced machine, but chooses the cMBP instead - that wouldn't be a very wise choice.
The cMBP was my 1st Mac. As a student, I could only dream of affording the model I wanted - (16gb RAM; i7; 512SSD). But I could afford the cMBP there and then. And over the past (almost) 3 years, I've been able to upgrade it to where I have a machine (with those same specs) that handles whatever I throw at it, flawlessly.
My next Mac (disregarding the last-of-the-quad-core-Mini's I picked up 6 months ago) will probably be a 13" rMBP, and probably the 8gb 512 version. And whereas now, even if I were starting out in the Mac world - I don't think I would get the cMBP (given its age) - but were its price to drop significantly, I might very well have given it a close look. It's a gateway drug to the Apple Mac world. If it's cheap enough - it still has something going for it, imo.