SIMON COWELL didn’t ask for the job, but en route to becoming the only voice that consistently matters on “American Idol,” he has established himself as America’s critic in chief.

Admittedly, as honors go, it’s a mixed bag. Critics have never enjoyed an especially glowing public image, with the most memorable fictional incarnations embodied by the amoral Addison DeWitt and murderous Waldo Lydecker, as played by George Sanders and Clifton Webb in “All About Eve” and “Laura,” respectively.

Both those characters reveled in their roles as assassins and intellectual bullies — the most ruthless and heartless fellow in the room but also, mercifully, the wittiest.

“I am a critic and commentator,” DeWitt says by way of introduction. “I am essential to the theater — as ants to a picnic, as the boll weevil to a cotton field.”

“I’m not kind, I’m vicious,” Lydecker harrumphs at one point. “It’s the secret of my charm.”

Indeed it is, just as Cowell — adorned in a similar snotty British-ness — has become renowned for bluntness bordering on cruelty as he goes about eviscerating hapless contestants.

Look a little closer, though, and Cowell is providing an actual guide to critical analysis — the kind sorely lacking in the ramblings of his fellow judges, Randy Jackson and especially Paula Abdul. For all the “judges” fox-trotting around reality TV these days, Cowell is the only one who can truly articulate not only whether he likes something but the why of it — a glint of reasoning amid the “Idol” audience’s catcalls before that always-deflating moment when host Ryan Seacrest’s lips begin to move.

COWELL’S SIGNIFICANCE in this respect has been magnified by the gradual disappearance of intelligent criticism elsewhere in the broadcast space. Leonard Maltin’s informed views are seldom afforded time on “Entertainment Tonight” anymore unless someone old and famous dies, and most local TV stations have traded in critics for red-carpet butt-kissers — a la KABC-TV’s “entertainment guru” George Pennacchio — or, amid budgetary constraints, no dedicated entertainment reporter at all.

Nowhere has the state of criticism suffered more than on “Ebert & Roeper,” the syndicated movie-review program that for years carried the critical standard in much of the public’s eyes. Roger Ebert’s absence while battling salivary cancer has dealt the program a major blow, forcing sidekick Richard Roeper — whose footprint was already so light it’s not unusual to hear the show still referred to as “Siskel & Ebert” eight years after Gene Siskel’s death — to keep the sparks flickering with “guest critics,” a term that’s often used generously.

In the show’s most recent “Anybody can do this” installment, Roeper shared the balcony with rocker John Mellencamp, who gave every movie a “thumbs up,” compared the just-released thriller “Vacancy” to “Rear Window” and said he didn’t flinch at seeing “the guy from ‘The Sopranos’” (that would be James Gandolfini) in “Lonely Hearts” because — ta-da! — he doesn’t watch the show.

Please, Roger, get well soon, and thanks, John, for proving that an opposable thumb is a terrible thing to waste.

AMID SUCH BLATHER, listening to Cowell channel DeWitt sounds all the more refreshing, tackling entertainment’s relative worth in a way that isn’t overly fawning or hideously fanged — the current polar extremes, with precious little between blowing air-kisses on one end of the spectrum and rummaging through celebrity trash to generate TMZ.com items on the other.

In “Laura,” Lydecker — who doubles as a radio host — boasts about wielding a quill “dipped in venom.” While there’s no modern broadcast equivalent, Cowell’s clear delivery places him in the stratosphere by default, demonstrating that it’s possible to register a critical opinion that doesn’t require stooping to conquer.

Being witty on TV isn’t as simple as it appears, but “Idol’s” enormous success and Cowell’s central role in perpetuating it should inspire a hunt for more voices of that variety.

Until then, the balcony remains open and generally occupied, alas, by rubes that belong in the cheap seats.

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A clarification: Last week’s column on focus groups mentioned “Everybody Loves Raymond” among programs that tested poorly. Although CBS assembled a report that compiled negative responses when the show was struggling in the ratings, overall the test results were positive.

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