Apple's JavaScript implementation is based on KJS as well. Arguably, Microsoft was hostile towards open source in general at the time, while Apple simply stole open source software.
It is not theft to use open source software in accordance with its license.
Legally they might have done the minimal amount necessary to not violate the license, but morally they've been a huge dick. "We have to open source our modifications to the code base, so here you get exactly one tarball of uncommented stuff."
That hasn’t been true for many years so what exactly is the complaint?