This requirement is new to the 2008 NEC.
Here is what 210.52(E)(3) says:
"Balconies, Decks, and Porches. Balconies, decks, and porches that are accessible from inside the dwelling unit shall have at least one receptacle outlet installed within the perimeter of the balcony, deck, or porch. The receptacle shall not be located more than 2.0 m (6? ft) above the balcony, deck, or porch surface.
Exception to (3): Balconies, decks, or porches with a usable area of less than 1.86 m2 (20 ft2) are not required to have a receptacle installed."
The exception states that if you have less than 20 ft2 you don't need a receptacle.
Chris