Cortex-strings is a year and a half old already, and is not in a single upstream libc. Upstream integration where, Ubuntu?
They at least patch their own eglibc with it, so one can use the patch if one knows where to look for it. Having to link an extra lib doesn't really work out, just ask Intel and AMD about their optimized string and math libs.
Canonical is a commercial entity. they don't want to make Linux better for ARM, they want to make Ubuntu better for ARM. Their goal is that you run Ubuntu, not any other Linux distribution.
Well in progress of making Ubuntu better for ARM they are also making Linux better for ARM by working upstream with Linaro. They are in no way trying to make it harder for other distributions to support ARM.