Commercial packages such as Matlab still need ld.so.1 and old libc5. So I believe ld.so.1 and old libc5 should be indcluded in the default installation, although MathWorks are certainly at fault here for not upgrading... More information here about Matlab on Linux here: http://www.mathworks.com/support/solutions/data/26704.shtml
It is not included on purpose. We don't want to fix obsolete libc5 bugs for ever. glibc is being used for more than 4 years now solely. If Matlab cannot rebuild their software against newer libraries, you can always install ld.so and libc packages from 6.2, there should be no conflict with any files in 7.x. It should work just fine, but it is definitely not supported.