1: I'm cheap lol
While that may seem like a semi-valid reason, there are other things you are leaving unconsidered.
2: I find $15 a month ridiculous considering you have to pay for the game as well which is 30-50 depending on where you buy it, not to mention expansions
Considering WoW has effectively replaced and haulted the past, constant stream of games I bought, it's probably saving me money in the long run. New games are generally $30 - $50. Even if one kept me entertained for two months (that was rare), I'd still break even by paying for a monthly WoW subscription fee. I can honestly tell you I haven't purchased a game in the 1.5 years I've played WoW. It has also replaced other forms of entertainment. I used to buy/rent movies a lot. I think the only ones I've purchased in my time of playing WoW are Dune, The Chidren of Dune and Underworld: Evolutions, which totals to about $50. I'm still saving money.
WoW is an emensely intricate and complicated game. Considering Blizzard maintains server farms that get more traffic than almost every internet site on the planet, I think the $15 is well worth the stability they are able to maintain.
3: Even if I wasn't cheap, I don't have a job at the moment to pay for a play to pay game that costs $15 a month ( I'm only 16 so I'm not overly enthuasitic about getting a job yet when I can sit on my can and play video games all day for summer break 
)
Pfff... I had a summer job when I was 14! It paid $8.50/hr too!
