There are!
It's a licensing issue; people claim they own particular ways of doing sums, and are backed up by legislation.
Ubuntu cannot distribute those codecs, not without paying money to the codec "owners" and that would mean Ubuntu CDs cannot be freely given away and redistributed.
The codec "owners" allow end users to install their software themselves -- they want their codecs used after all; they mainly want to charge media companies for using them -- and Ubuntu makes this quick, intuitive and easy. This hardly "puts ideology over usability".