Yes. There's a finite distance you can run this train of thought, but i'll continue: At what point does your system stop being Ubuntu, and start being identica

Yes. There's a finite distance you can run this train of thought, but i'll continue: At what point does your system stop being Ubuntu, and start being identical to someone's WindowMaker distro, customised to use ubuntu repos? (Lots of desktop debian users add ubuntu repos for the occasional package.)