Well considering that QOS was a disappointment for many, it's not surprising that people want Skyfall to be better than that. If it's worse or the same as QOS, then a lot of people won't think Skyfall is "good" and won't be happy. It's not really about trying to compete with other movies in the series such as CR. It's about having a certain level of decency, which many felt that QOS fell far below. The reason people cite CR is not because it is the yardstick, but just that it was the last and most recent decent Bond film, and also part of Craig's run, so yes, people will look to that.