That's interseting, usually it's the Alaskan Game Stops near me that don't have them. I went to a Game Stop last night and there was a shiny new stand-up selling game time cards of all types. The back of the cards are set up to be activated on Game Stop's system, so any card you purchase there *should* work.
As for why SOE does promotions like this? It's one of the ways they convince stores to carry their cards, with exclusive promotions.