Tragedy said:
What I am trying to say is that WoW has a lot of things going for it, but Blizzard aren't capable of maintaining or exploring that potential. THAT'S what's causing the sub loss, not age. They have tried to lessen the effects of age on the graphics which shows. It's still a very nice game to look at. I covered other things (like old players staying) in my other posts.
WoW does have a lot of things going to it, and probably is still the principal draw in the (extraordinarily stagnant) MMO genre. There are a lot of reasons for that, and for the problems with the genre as a whole.
It is disingenuous, however, to hand wave age as the over-riding factor behind subscriber entropy. There isn't a game in existence that cannot wear out its welcome through excessive play, and the man-hours poured into WoW over its decade plus of existence are staggering. How many iterations can you make on that core formula before your play mechanics begin to grow stale? How many changes of venue, how many new classes, how many revisits of popular lore characters, before the fact you're still leaning on the same game play pillars becomes a problem? How many of the "me too" clones of Everquest's loot level treadmill failed...not because they were "bad games"...but because they were exploring an extremely tired formula?
There are lots of arguments about whether or not this quality of life change made WoW better or worse, or whether a particular streamlining robbed the game of important complexity or banished an annoying chore. It all depends on the gamer in question. Wildstar tried to capture "Burning Crusade era WoW" by revisiting hostile attunements and aggressively stratified player accomplishments (ideas a WoW player was recently triple gilded for after waxing nostalgic about them on Reddit) and the idea went over like a lead balloon. Was Wildstar just an exercise in ineptitude, or is it evidence that things aren't as simple as "the game was better back then"?
While debates might rage over whether WoW is a better game when it caters to hardcores or casuals, is better off being streamlined or groaning under the weight of a thousand game play complexities, thrived more during "raid or die" or "welfare epics", needs forced socialization or more solo content, etc, etc, etc, the one thing that is universally true of every last person playing it is that everyone has a boredom threshold. That a sizable amount of people might be hitting it after ten bloody years is not surprising, even by the standards of a genre that celebrates time sinks and treadmills.
TLDR - Age is a factor. Even if WoW was the best game ever made, it would still be shedding players due to age.
PS - I went back and read your post...where on earth are you getting those CoD and Battlefield numbers?
Call of Duty has sold 141 million copies in the entire history of the FRANCHISE going back to 2003, a total of 10 titles sold across a multitude of platforms. The highest single title sales were 26.5 million for Modern Warfare 3. Battlefield sold a fraction of that, with the highest single title sales being Battlefield 3 at 15 million.
World of Warcraft sold ~14 million core boxes, and over 28 million expansion boxes (through 2013, does not account for WoD). This does not account for revenue from subscription fees. In box sales alone it rivals the success of the CoD franchise, given it is a mono platform game, and that is counting the core game as a distinct entity from its expansions. If you count expansion sales as part of the whole, it dwarfs any single CoD title, which have had the benefit of unique titles and advancing tech, not just iterations on an aging engine. It is one of the top 5 highest selling PC titles of all time. The total revenue from that ONE TITLE comes close to rivaling the
entire CoD franchise, and likely easily outstrips it on any single platform.
PPS - Through January of 2014, Skyrim had sold in excess of 20 million copies, putting it just shy of CoD's highest selling title. How exactly is it that RPGs are not "mainstream"?