The price difference from the MSRP (~$15) makes up for one additional month of play time in addition to the included month. WoW game discs and 2 months of play for $50? Great deal.
While the EQ2 deal is even cheaper, I recommend WoW over it. I've played a ton of MMORPGs, including both EQ2 and WoW, and I have to say WoW is the best I've ever played. It's easy to get into, extremely fun, and has minimal time commitment.