WoW is a harder game to just take breaks from.
For example, start a dungeon run in WoW and you're in for the duration, for the most part, unless you just bail out part way through and leave your hapless groupmates short one player, in which case everybody's time may have been wasted.
Start most dungeons in GW (at least with Heroes and Henches) and you can stop anytime, take a break, talk on the phone, eat dinner, and come back to the game later. You don't lose anything. You can even quit a dungeon or mission and do it later because you know you can always either find another group or that the heroes/henches will be ready and waiting to go with you.
These are
radically different game dynamics, in my opinion.
Recalling my days in WoW, there were a lot of late nights, missed dinners, ignored phone calls, etc. Maybe that was just me, but I just got tired of that after a while. Even in solo PvE quests in WoW, if you are working your way toward some boss or other, you CANNOT STOP mid-quest because everything you have just killed will respawn on top of your character and/or you will get booted from the WoW server for being afk for too long (I think the timer for that is 30 minutes).
GW is thus inherently more amenable to people who want to take breaks and who have a more casual (or less addictive) approach to gaming. I also very much appreciate the fact that in virtually any mission or area in GW, I can hold my own along with players who have invested many more hours in playing than I have. My gear is on a par with theirs, in other words -- though my playing skill might not be
In WoW you have a kind of "elite player's class" that has developed; at the higher levels/end game content in WoW, you are at a serious disadvantage if you don't have all the best "tier X" gear -- but to get that gear requires more time and effort than most players have to give.
I am not harshing on WoW; it's a good game in my opinion -- just not as real-life friendly as GW is.