When I couldn't load Sunday's puzzle, I went to washingpost.com, got very confused at the sight of a puzzle I'd already done, and figured I'd get the real story from Orange. Sure enough, her entry for 4/6 says, "And then there were five. No more Sunday Washington Post puzzle to enjoy—Washingtonians will now be getting Merl Reagle's crossword, which I (and you, if you like fun crosswords) already solve in its Philadelphia Inquirer incarnation."
Google reveals there was also something about it in the WP itself. They don't explain about dropping the old puzzle, only about picking up Merl's.
Not only that, they don't seem to have a .puz option any more. You either use the Java applet or download a PDF. Weird, since the .puz obviously already exists for the Philadelphia Inquirer.