Total lies? What would… oh, do some companies do that? Does Dell only give Best Buy certain models or something? It's bull honkey. Best Buy has nothing the Apple Store doesn't. The dedicated GPU comes on if you're doing something graphical with the computer. Under light loads, the dedicated GPU is turned off and the integrated one takes over.
About This Mac, More Information, System Report, Graphics/Displays. It'll show you both GPUs.
*blink* What did it show?
You're sure it was a 15", you're sure it was the most recent model, and in going here:
you didn't see anything Nvidia related?
Also look for the Model Identifier in System Report > Hardware Overview > Model Identifier.