I can go back as far as the early 70's and whilst Maine Rd wasn't as bad, this trait was still there. Most of the time the prevailing attitude at least until there is a major key moment in the game is that sort of stereotypical Manc type cynicism. That said, when it does go it really goes. Obviously really big moments like Aguero 9320 or the preceding 1-0 in the derby but one of the loudest all round the ground ones I recall was around 94/95 when Newcastle visited MR under Keegan. Sellars scored first for them and then we went 2-1 up (Walsh debut goal?). I've rarely seen MR like that. Even a few Geordies who'd got tickets in the City part of The North Stand we're commenting ' never realised this place was as mad as this' (paraphrased).
There are other contributing factors I think. Firstly that ingrained hope it will go well but expect it to go wrong whilst arms folded mentality. Secondly, because of our long period of under-achievement and despite a loyal core, the percentage of home match attending fans that are in the late teens, twenties, early 30's, the one's who generally give it wellie, is maybe a lot lower than other clubs. This may change over the next 5/10 years with a sustained period of success as we attract local fans that might otherwise have opted for United.
Maybe too it is just that the profile of a large chunk of fans at other clubs is simply more 'blindly fanatical' Liverpool being the best example e.g. the pre- City/Chelsea coach parade and appealing/squealing every decision against them, whereas ours is one more of steadfast loyalty blended with self-criticism/moaning and the occasional 'roof-off' moment.
I had an interesting discussion in the pub about City fans and a group of us came to the conclusion that we are Joy Division to the Scum's New Order, we are the Fall to their Stone Roses, we are undemonstrative, very cynical, quite English and unshowy in comparison to their mawkish gobby strutting and posturing.