In Wow you play a paladin. Dot-Stop-Don't ask more. Did he have parents? Why did he become a paladin? Try asking that to a few people on wow. Besides on the RPrealms you will probably just be looked at as strange. Wow isn't about character development, it's about leveling, killing baddies and having the ubergear.
WoW's storyline and the reason that characters are there is far more in depth than anything that PS has. Novels upon novels have been made and released by Blizzard detailing a massive amount of lore. The online version is chalk full of lore with every quest you do.
The difference between WoW and PS is that PS, the player has to make up all the events and RP arcs they do in game, whereas in WoW, from the moment your character is created you're being thrown into the lore of that game and you chose to either follow along with it as you quest, group, and travel the world, or you simply choose to ignore it all and bash endlessly away on monsters and never experience 90% of the game's content.
That sounds no different from what happens in PS. If PS was different, then why is there a new thread made every month about how players that only grind away in the mines or "powerleveling" their toon's skills are ruining the game?
Don't bash a game unless you know what you're talking about. The term 'Roleplaying' has many different definitions. Just because you don not approve of someone else's definition, does not make their definition wrong.
I've been with this project for 5+ years now, and just as long, have I played WoW, both the MMO and the RTS series created before it. In the MMO, I'm ranked in the top 20 out of 25k toons on that server, on the oldest server Blizzard has had up and running since the beginning of the MMO's initial release. In PS, my characters have been involved with nearly every major event this game has had thus far, but because once people find out who the player is behind a certain character, every time they meet another character they know that is being controlled by that same player, they treat all the characters the same, even when the characters are vastly different, I choose long ago to never reveal any of my characters' names.
I've seen people come and go, in both games. Guilds are forged, and guilds are disbanded. Both games have players/characters that are known and recognized and looked up to.
The only difference between PS and WoW, is that in PS, there is a very vocal minority that wants the game to simply be a 3d chat room where they can sit endlessly in a tavern talking away tales of great adventure to their friends, rather than going out and actually playing the game and actually doing said adventures.
If you don't want to call WoW a roleplaying game, then I don't believe you can call PS one either. You might as well call PS a 'sit around in a virtual world telling tall tales to try and impress everyone else with your vast imagination' game.
Oh and, to back up my claims with fact;
link to my WoW character:
http://www.wowarmory.com/character-sheet.xml?r=Whisperwind&n=Kintwolink to my toon's ranking:
http://wow-achievements.com/Person.aspx?region=US&Realm=whisperwind&Name=kintwo (overall ranking is out of all players in the world; currently 11.5 million players. Regional ranking is just North America, realm ranking is just out of players on the server I play on; currently about 25 thousand players.)