That too is true. Most of the audience had little knowledge of Iron-Man to have expectations. Joker was in tune with the character and what people expected. Dark Knight was very much what people expected of Batman. MoS was not what people expected of a Superman movie.
Joker making a fortune and WW being very critically acclaimed even with a lot of the subject matter being the horrors of WWI, you can't just explain away the success by saying audiences just want fluff.