I usually enjoy AC Grayling, but I'm a bit puzzled by his letter to the Guardian. It may help to bear in mind that my undergraduate degree is from UC Irvine, for many years the home of all things Derridean--including, for a quarter each year, Derrida himself. Deconstructionist criticism in its "purest" form, if there was such a thing, often had remarkably little to say about gender, race, national identity, or anything else that sounded vaguely historicist. In its applied American form, it generally amounted to hyper-intensified close reading, a practice more amenable to discussions of metafiction than to feminism. Language was the big thing, not cultural criticism. Moreover, because it was in so many ways (again, in its applied American form) a souped-up New Criticism, deconstructionism tended to emphasize not the non-canonical but the very canonical indeed. That is, deconstructionist critics tended to go for the jugular of literary works with already-proven pedigrees in the area of complexity. Anyone who wandered through the UCI English Department's assigned readings in the bookstore during the late 80s or early 90s would have noticed just how "traditional" the reading assignments were. (I can still recall, with some exasperation, Andrzej Warminski's suggestion in the student paper that we shouldn't toss the canon--just deconstruct it. This prompted one of my few forays into the world of letters to the editor.) By contrast, the far more literary-historical faculty at the University of Chicago assigned a much wider range of works. Now, other people seized on deconstructionist techniques to shore up their own particular projects, including the project of dismantling the canon--the "postmodern allies" of whom Grayling speaks--but the deconstructionists pure and simple tended to fixate on literature's self-reflexive qualities. Postcolonial theorists, feminists, Foucauldians, historicists of various stripes, and so forth, all seem to suit Grayling's bill rather better, but many of them have had a few bones to pick with Derrida; one thinks of early complaints from specialists in African-American literature.
UPDATE: Oh, and before anyone jumps on me, I'm a big fan of close reading, and by "remarkably little" I don't mean "there should have been a lot."