There are a lot of wonderful points that have been discussed on this thread.
First, I think that for a lot of corps the financial reasons were paramount in their minds. It wasn't fiscally responsible to purchase another set of G horns. Having marched only G in DCA and DCI I do know what it is like to manage a G bugle. The sound is open, and raw and the sops do pop in the upper register. But now that I instruct a junior Bb line I can really see and hear improvements.
Second, Here is my suggestion for a horn line....
Trumpets/Sops in G
Mello is F
Bari/Euph in Bb
Tuba/Contra in Bb
A quick story....
I was on the road last summer and as I was walking down the stands after our performance I saw a middle aged gentleman sitting down, furrowing his brow and not clapping like the 2000 others around him screaming their heads off. I was genuinely interested in why he was not pleased. I stopped and politely introduced myself as a brass instructor for Southwind and asked what he thought of our show. He said "It is trash" I took the bait and asked why. He told me that because the corps was playing Bb horns he refused to clap or applaud because he believed that you could only appreciate drum corps in G. I said I was very sorry and I told him to enjoy the rest of the show. I'm sure he never clapped, because nobody was on G horns that night...
My only beef with this argument is that occasionally we take it too far. If you are not a supporter of Bb that is your opinion, but please don't take it out on members of any corps. 1. it is not their decision which key they are in 2. they work hard to entertain and perform for you
I hope I was able to shed a little bit of insight into this discussion. I love drum corps, period. And I am sure that before I die, there will be many more changes that I may or may not agree with. But the one thing that connects all brethren of drum corps is the common bond of hard work, long days, sweaty nights and the memories of a lifetime. No Bb, G, Amps, 3 Dimensional Drill, Flying Color Guard or whatever the drum corps path has in store of us will ever take that experience away.