The fact is that over the last 30 years, things have changed and if you were to read the forum of any 'big' club, the atmosphere debate features. Small clubs in small grounds these days can't believe their luck that they are playing in the Premiership (it never used to be like that). As a consequence, their fans go mental all game. As an example, Selhurst Park never used to be a ground renowned for its atmosphere, but it seems that it has been transformed into a cauldron. This is down to the fact that Palace have been out of the top league for a decade. It's the same at Stoke, Swansea, Cardiff etc. Double the size of their grounds, give them 10 years in the Premiership and you'll find that the atmosphere at their grounds isn't quite so intimidating.
The more used we get to success, the bigger the ground becomes and the more we become established as one of the 'Big Four', the more sanitised the atmosphere will become. It's not the fault of City fans per se, it's a phenomena that effects English football. Alternatively, we can move back to a Maine Road esque ground and struggle for survival with the occasional relegation and experience a better atmosphere.