Normal A/C draws in air from outside (100*) and tries to cool it down to a point where it is comfortable to you. Recirc draws the air from within the car (65*-75* once the normal mode gets it to this temp) and tries to cool it down to a point where it is comfortable to you. Point A (front of car) to point B (inside of car) is not very long of a travel to get that hot air cold. You work your A/C harder leaving it normal mode and it you will never achieve the max coldness that you can get by leaving it in a mode that is always trying to cool the outside temp. It is no different than the A/C in your house. The house A/C is recirculating the inside temp and not the outside air. I don't think any of you would open your windows and front door to keep your house cool once your recirc got your house cool.
actually.. modern furnace & A/C systems draw in outside air.

It's mostly for combustion of the furnace in the winter, but serves to add fresh air into the system during the summer. As well, EVERY commercial/Large building out there draws a high proportion of its air from the outside to keep the air as fresh as possible.