Totally random: wiki says Ordinary People "...is the last Best Picture winner without a Film Editing nomination..."

'Best editing' is even more a popularity contest than 'best picture.'

Except there's no correlation between the two categories: editors nominate editors, whereas all Academy voters nominate Best Picture, regardless of whether they know jack about editing or not.   There's no secret society within the Academy that makes adjustments to the overall outcome.

Usually you see the mechanics of the process when things conspicuously DON'T get nominated for something, a la Prince of Tides getting Best Pic/Best Actor/Best Actress noms because the Academy overall liked the movie and the actors' branch thought the performances were worthy, and yet didn't get a Best Director nom because the directors' branch apparently didn't think of Barbra Streisand as being one of the club.   

There are so many factors that it'd take a Nate Silver to crunch the numbers and see if there's any particular reason behind the editor/Best Pic factoid.   I'll bet it's a combination of factors rather than just one, or maybe even just a lengthy run of concidence that will end next year.   But it's definitely not because somebody in the back room is "deciding" it, tho.

When it comes to narrative editing, it's also knowing which elements of which takes to use as to craft an actor's performance as well.  Just because the director yells, "Print!" after a take, in no way is that to be set in stone.  Throwing shots out of sync, even using elements of a take that are before an actor even knows the camera is rolling, are things editors use to define the scene.

I come from a documentary background, and one trick I would always do is start rolling before an On The Fly interview, but still act as if I was setting something up with the camera (turning the tally light off was integral for this).  The subject would usually tune me out until I started asking questions, and sometimes you could get some very expressive looks out of them.

Editors are problem solvers.  If you see a film with no major problems, chances are the Editor is responsible for fixing a few of them.

Or - since movies lately have tended to have more than one editor, more editors have been getting nominations, and being nominated is the primary way you become an Academy member in the first place.   

So as the percentage of editors within the overall Academy membership grows, relative to other specialties (actor/director membership wouldn't be subject to the multi-nomination effect) their edit-aware votes may be skewing the Best Picture noms toward the better-edited films...

I'm totally spitballing the above, might not actually be true at all.  Just saying that there can be plenty of non-intuitive explanations for things.   

Seriously, either Nate Silver or the Freakonomics guy could probably get a whole book out of finding the hidden oddities of how Oscars get awarded.  Problem is, there's very little data to crunch - the Academy never reveals the actual vote numbers.   So we'll never know if Shakespeare in Love beat Private Ryan by one vote, or a thousand.

Most people seemed to agree that Scorsese's THE DEPARTED win was really more of a lifetime achievement award, too.

Likewise it's pretty commonly accepted that RETURN OF THE KING's Best Picture Oscar was really being awarded for the entire series, but they didn't want to give it to the same series three years in a row so they just let the last stand for all.