It's not rewriting parted. Parted can't handle all modern storage technologies as it only deals with partitions which are only one part (pun intended) of the picture. In the [your favourite distro here] installer the UI calls out a *suite* of tools just like Blivet-GUI does. Previously in Fedora this was all piled into Anaconda - but now it is split out into this "Blivet-GUI" thing.
If you bothered to read the articles or browse the source you'd know that it depended on Blivet and subprocess calls to normal system utilities. Blivet has been around for at least two years already and has matured through its use in Anaconda. Anaconda has been around for many years and has always (AFAIK) depended on Python. Nearly every Linux distro (and other Unixes, OSX and even Haiku) come with Python by default. Most installation environments can use whatever they please without impacting the resulting system so even if you didn't want to install Python (or the more concerning GTK, IMO) you don't have to. This person was not engaging in NIH - they were simply writing a new GUI to an existing tool to allow for better integration, easier modification and fewer dependencies... Shock horror! OMG WHAT AN IDIOT RITE???
This mindless Red Hat bashing has really gone too far.