I don't get why you people go on and on about this.... You probably have a misconception of what "class of such and such" means! If you know, you wouldn't be criticising the way you did.
Denis Irwin does not belong to the 'class' because he was not through the academy from the age of 12-13 like Giggsy, Becks, Scholes, Butt and the Neville brothers. And Denis Irwin was and still is a very respectable member of the United family. His loyal fans are probably more than the total of the class of 92 combined (well not quite but you know what I meant! No one dislikes Irwin. Period)
When these players were mentioned collectively, they are the class of 92, when its the time when they 'graduated" and excelled (from as school boys within the United Academy system). They famously helped the club win trophies in defiance of the infamous reference "you can't win with kids". That's how powerful these youngsters have become. The rest of the team contributed but they were not from the academy (or not as important players in comparison) hence were not referred to as such.
These players also carried on to make the club more and more successful for a very long time and were involved in the treble year....
Don't know what the fuss is all about.