Most schools operate this way. I can't think of any major colleges, at least in Texas, that do not have a COM. I know music majors and teachers from many schools. The entire UT system covers COMs. UTA, UTSA, etc. Texas Southern has a COM. most community colleges even provide departments.
Other schools come to mind with very nice departments (maybe no marching band)...Texas Weslayan [sp], west Texas A&m, etc
Let's not be so naive with the spirit argument: participation would drop dramatically - for better or worse - if the requisite was removed. And those high school kids, many of them, are doing it because they get to avoid having to do P.E. and get an end-of-year band trip to look forward to.
**addition
Most high school bands spend about 2 hours every week day rehearsing. This includes their class block, plus the extra 1.5 hour morning practice that requires them to be at school by 7 am...maybe 630 for some. This does not include the extra time they arrange for weekly sectionals or the saturday run-throughs/review. Nor the alone time they spend practicing their music at home.