What the likely mean, is that newer versions of pip support newer platforms underpinning the binary packages.
Python binary packages are a bit of a kludge, they take a binary built on a base platform like CentOS 5, and use tools like patchelf to take all the libraries that they dynamically link against and re-wrap them in a new package.
Until about a year ago, CentOS 5 was the newest base platform available. So if your library needed a glibc feature or some other library feature from the past decade you were SoL.
