Originally Posted by Trumpet Dad

I believe it is so that you do not have to learn new fingerings for each different pitched trumpet. All of the fingerings are the same whether you play a B-flat trumpet, C, D, E, or E-flat.

A 'C' is fingered the same (all valves up) on any trumpet. The sound that comes out of the bell however, will be the pitch that the trumpet is keyed in.