10-20? what a load of rubbish. I've played WoW and besides the stream of mounts and pets you can purchase WoW you can go half a year without seeing anything new at all for your $15 a month.
Meanwhile gw2 ->
http://wiki.guildwars2.com/wiki/Game_release and that's 13 of them. Living story chapters, new zones, mini games (some not so mini, SAB for example), new armour, new weapons, guild missions (bounties, rushes, missions, challenges), new dungeons (9 fractals + 4 others), new quests, new ingame functions, new rewards, new skill systems (not just revised but NEW), jumping puzzles...
big updates in WoW are what? a raid with a few quests stuck on that can be completed in a few hours if that. The raid? just go LFR and see all that big content patch within a week. gee whiz I'm overwhelmed with things to do.