QUOTE(barry-clari @ Aug 21 2009, 10:35 PM)

Many reasons : one major one is to save memorising a load of different fingerings. Clarinettists can be expected to play instruments in Bb, A and Eb, knowing that the fingering for, say, written B is the same on all three instruments makes my life so much easier.

It still strikes me that over all this time, no one has ever thought to attempt some sort of rationalisation so the written note is the note that's sounding, whether this could be accomplished by a slight adjustment to the design, I don't know.
I find it quite astounding that no great composer has said "Actually, it's a right royal pain in the rectum having to transpose stuff for the woodwind section", and hence pushed through some sort of tweaks to design!

I'm sure I'm missing something hugely fundamental here...