Dead parents are so much a part of middle-grade and teen fiction at this point, it's not even the "in" thing. It's not "au courant" or "en vogue." It's just an accepted fact: kids in books are parentless.
But I don't accept it, because you know what? It is not believable that so many kids are missing one, if not both parents. Slews of them! Hundreds! To quote Oscar Wilde, sort of: "To lose one parent may be regarded as a misfortune; to lose a parent in nearly every children's book looks like lazy writing." (I assume that is what Wilde meant.)
Of course, dead or removed or simply not-very-involved parents are almost the necessary ingredient in a good adventure or fantasy story (the Swiss Family Robinson aside). Sales's article did make me do a quick mental review of some of my old and current favourites:
The Lion, the Witch and the Wardrobe (C.S. Lewis) - absent parents, guardian figure who subtly encourages adventure
The Sword in the Stone (T.H. White) - obscured parental situation results in effective orphan status, one bumbling guardian figure, one guardian figure who subtly encourages adventure
I Capture the Castle (Dodie Smith) - dead mother, obdurate (possibly mad) father, one of the best step-mothers in fiction. The Mortmains remain my favourite fictional family.
Ballet Shoes (Noel Streatfield)- three orphans, collected by an absent eccentric, given two female guardian figures and a handy mechanic.
When You Reach Me (Rebecca Stead) - absent father, father stand-in, mother. Less mad-cap than the Mortmains, but a beautifully drawn group of relationships.
Summerlands (Michael Chabon) - dead mother, grieving father (who needs to be rescued)A Wrinkle in Time (Madeleine L'Engle) - absent father (who needs to be rescued), preoccupied mother
Island of the Blue Dolphins (Scott O'Dell) - girl and her brother left behind after tribe abandons island
His Dark Materials (Philip Pullman) - secret parentage disguised as orphanhood; helpless mother and missing father
Tender Morsels (Margo Lanagan) - disguised fatherhood, close mother
How I Live Now (Meg Rosoff) - exasperated father, text-book stepmother, guardian figure hurriedly absents herself
The Knife of Never Letting Go (Patrick Ness) - tragedy atop tragedy.