I suspect that SuSE and Oracle may have better luck getting newer kernels to work with older userspace, in part because they have kernel developers on staff to prepare patches to newer kernels that fix the incompatibilities they find, and in part because they have more influence on the kernel development community. If, for example, SuSE wanted to fix sysfs in 3.0 to accommodate older udev, they'd have to find someone to write a change to sysfs stuff, and they'd have to get the sysfs maintainer to sign off on it, and they'd have to get the stable maintainer to include it. At the time, this would have been Greg KH getting himself to write a patch, and convincing himself and himself.
Also, SuSE intended from the release of SLES 11 with 2.6.32 to be able to upgrade the major release of the kernel, and exerted pressure to keep things in mainline from breaking SLES 11 userspace. It's a lot easier to NACK patches and revert commits that haven't seen an official release yet than revert behavior changes where different programs may have come to rely on each behavior.