Except there's no exception here; the instrument is the person's own, not the schools. (And a previous poster indicated that the students themselves buy their instruments, therefore there is no irregularity.)
Your argument is like saying that because someone shows up to gym class with green socks [and everyone else has white] there is no discipline; that's just ridiculous.
Orchestral discipline has nothing to do with collective conformity, except in the execution of the music.
Obviously you’re no serious musician.