The relationship between Debian and Ubuntu is more akin to that between fedora and RHEL.
Having a different focus than fedora, in fact, one could say almost radically different[1] hasn't stopped Redhat from contributing people, hardware and support to fedora -- leaving the volunteers to focus on contributions -- be it by code or as you point out documentation.
Help with 'administrative' or grunt-work tasks goes a long way in large OSS projects and Ubuntu/Cannonical simply haven't stepped up where they should have.
[1] for business vs for developers, cutting edge vs stability, ..etc
Red Hat have been pretty smart with the whole Fedora/RHEL/CentOS progression. You get to mess with cutting edge stuff in Fedora (and Fedora Silverlight), and then take what works to fold into RHEL. Then you rebuild RHEL into CentOS so people use the free and binary compatible version of your product, which leads them to use the supported/sold version in production.
Having a different focus than fedora, in fact, one could say almost radically different[1] hasn't stopped Redhat from contributing people, hardware and support to fedora -- leaving the volunteers to focus on contributions -- be it by code or as you point out documentation.
Help with 'administrative' or grunt-work tasks goes a long way in large OSS projects and Ubuntu/Cannonical simply haven't stepped up where they should have.
[1] for business vs for developers, cutting edge vs stability, ..etc