Well to answer your first question, they sell pre-overclocked cards so people that are new to building/not comfortable with overclocking them selves can buy a card where the manufacturer has done it for them, plus if you overclock it voids your warranty. Lets say its Fool Proof overclocking. In the end youre paying $20-$50 for a pre overclocked card... Some more advice with Cooling on cards, If you have a very small case a blower/turbine fan is better (refrence design) because it takes the air straight from the case and blows it over the PCB and GPU then the hot air goes out the back of you're case so it dosent heat anything else up. If you have a "larger case" (Normal ATX or Larger) I would get a after market cooler I.E TwinFrozr from MSI or Direct CUII from ASUS, or ACX from EVGA Windforce from Gigabyte and so on.
Hope this helps,
Have a Great Day!