I'm still not sure what the set-in-stone rules are for what most people in these forums use to classify a "true MMO." It seems like the social aspect is important (which the critics claim GW does not have--not true), or the ability to run into players in the field (I'm not sure why this is so important). Actually, I spend most of my time in GW chatting with firends I've met while in random pick-up groups, farming...and questing on occasion just to advance. It actually took me several months to get my first character through the end of one campaign...as I got so distracted by interacting with other people and figuring out new and unusual builds for my several characters. I barely even PvP, but it's an entirely new aspect I haven't exploited--and that I'm not paying a monthly fee to ignore...
My question is: What defines the social aspect of a game? I've actually met a couple of really good people online and we'll hold ongoing discussions, we know a few things about our personal lives (how is this not social enough?), run around and goof off a bit, etc. Why is it necessary to run into people while questing to classify an MMO as a true MMO? This is why I don't play WoW; b/c I would have to get too involved to progress in any way, and I prefer to mix up my free time with other things in life. (Not that I'm saying WoW players are any more geeky or too dedicated...just that I think to be competitive you have to spend more time online...much less the idea of getting what you pay for in respect to monthly fees). That being said, to truly get everything out of what GW offers, you would end up spending ~$100 per year on the 2 new campaigns that are released.
I also have a job, make good money, and wouldn't consider myself cheap; but there is a limit to what I can justify spending my money on a monthly basis. (However, I also take the time to bitch at the cable company when appropriate, in order to get my monthly rates reduced to an acceptable amount). So saying someone doesn't want to pay monthly fees for an online game misses the point of why most people object to paying those fees. GW covers just about everything I look for in a game these days; and I think that expalins why people have different preferences for certain types of games. (I've never bought an FPS b/c I find them boring with no replay value after a few weeks...and eye candy is just an excuse to spend another 1-3k on a new rig) But, too each his/her own of course.
In the end, the cost per play is negligible between the two as you essentially pay the same amount on a yearly basis to have full access to either GW or WoW. This is simply a matter of different business models b/w Blizzard and Arena Net in how they advertise and produce their games. I rejected Blizzard's model b/c I see a monthly fee as a reminder that I should be devoting a certain amount of weekly time to this game in order to get my money's worth. Really, it's all about psychology and approaching players based on how they value their time and money...and of course their game style differences...
And GW is nothing like Diablo. I think most people that claim this have probably played GW for a day and immediately write it off as being too derivative. You do have to get pretty far in the game to really start enjoying it; so most will miss the more interesting aspects of strategy involved in the game if they don't spend a little more time with it.