See this and this and this (a 2012 release, no less, so they're still using it); didn't take much digging to find them. It's not uncommon (at least in the past) for HD and HDX to be in DD+ while SD is in DD 5.1 or DD Stereo. I saw one odd title where HDX was the only one in DD while HD and SD were DD+--I tested the 2 minute preview and it was true . Can't remember what it was.
EDIT: Poking around more through VUDU's catalog I find that plain old DD is pretty common, though not so much in releases of the last year or two. There are few real oddities--Batman Begins, for instance, is only available in DD Stereo at every quality level.