Maybe it comes down to where you stand on Apple products and Gruber but I'd say he was spot-on. The things that he mentions also stood-out when I read the article.
"The analogy of an Apple tax might sound facetious, but think about it. Median U.S. household income was $50,054 in 2011, according to the Census Bureau. That means a sizable chunk of that is getting diverted to Apple headquarters in Cupertino." Before reading the article and just Gruber's post I would've agreed with you that Gruber is niggling but it appears that the author is actually semi serious about there being an Apple tax.
Also, yeah, about "tax". It's used pretty loosely sometimes, John. Like when mobsters talk about protection money. Welcome to language.