There have been numerous threads and posts here related to the move to require uniformity in certain sections of orchestras. I have personally railed against this movement (as have others) claiming it smacks of elitism or snobbishness and eliminates all of the wonderful-sounding vintage trumpets from inclusion in these orchestras and, of course, reduces the listening pleasure of the audience.
However, I think that I have found the real reason for it. This clip is the clue. In today's world of not just music AUDIO but, more importantly music VIDEO, the impact of section uniformity has finally become apparent. As you watch this video (the shot of the trumpets in the opening stanza are a big hint), you will see that not only does the section require uniformity among the instruments, but even such things as height (and gender?) of the players plus nose shape and hair cut (look at the flute players - even when only one is playing). Also, as much as there is uniformity among the trumpets, the horns are almost as impressive - along with the trombones, the basses, the clarinets (with the bassoons in the way), the oboes, etc. I guess we live in a world where the image is everything. (But, they do sound nice).
[ame="http://www.youtube.com/watch?v=Qza92T805k4"]YouTube - Dvorak: Symphony No. 8 in G Major (IV)[/ame]