<<Probably an ego thing. I know you are a Heavy or a Super because your flight strip says so, in the same way that Concorde always checked in as "Speedbird Concorde 1" yes we know that you are but if you feel the need to tell everyone on the frequency then work away......>>
In the UK there is a requirement for crews to specify aircraft type on first contact with some ATC units. This is because airlines change type without informing ATC and it is essential information for wake turbeluence purposes.