Sorry, but if it is not a "check" (e.g., skill or ability) then natural 1 and natural 20 applies.
Granted, I had hope that Wizards would have been more meticulous in mentioning this in the next printing of the Player's Handbook. Personally, this was a grave oversight for both first and second printing, akin to having Dumb and Dumber editing the book.
No offense, but I've always have a vote of no-confidence when it comes to the Wizards' in-house editing and proofreading staff. They should think like rules lawyers.