Appealing to a broader market is a specific strategy. Nothing wrong with it all. It works for many other games. Clearly so for Blizz w/ WoW.
There is this psychological myth about Warcraft that it was at one point some serious, mature and deep MMO. Erm, it never was. Warcraft from it's RTS days to present has always been tongue & cheek, slightly juvenile and simplistic. That Blizzard have perhaps refined their formula now for the largest/broadest audience- sure.
Now I totally understand games made with that intention in mind may not be for you personally or a number of core gamers. Though I think is unfair to find fault in a game for targeting a certain or at least catering to non-core gamers. Esp. when it's as successful as WoW or Call of Duty, for example.
I wouldn't say Wizard 101 "goes wrong" for designing it's content for a lighter & younger audience. It's just not the the game designed & targeted at me is all. Same goes for WoW- it's just not aimed at me.