Didn't read the article, but I would like to point out a fundamental flaw in the reasoning in this quote. Graphic designers and usability engineers are not the same thing. Graphic designers are only interested in what is pleasing to the eye. Usability engineers are more interested in how the eye and the hand coordinate to complete a task. It's unclear whether IBM is accusing Linux developers of copying Microsoft's visual style (which, after being on a Mac, is shockingly unbearable), or copying Microsoft's interface style (which is for the most part the PARC-foundation stuff - buttons, dropdowns, dialogs, etc).
And, I've maintained since it was first leaked that KDE4 looks more like OSX than anything else.