As amusing as it is to poke fun at older people watching (or clapping on, heh heh) “Harry’s Law” and “Jesse Stone,” the anger unleashed by the decisions to end their runs exposes a serious point.

For a business built on communications, TV networks — along with most consumer outlets covering them — generally do a lousy job conveying the underlying rationale for relying on younger demographics, to the point of having practically given up trying.

The adults 18-49 demographic has served as the industry’s primary sales barometer for so long, we take it for granted. Moreover, the one broadcaster that dared second-guess those criteria, CBS, is enjoying enough success relative to its competitors as to voice doubts regarding the status quo less consistently and forcefully.

From a PR standpoint, though, the formula appears to make even less sense now, what with the median age for every major network except Fox hovering around or above 50, effectively disenfranchising half their audience.

Although they may not like it, mature adults can probably comprehend why movies cater to teenagers, recognizing the importance of opening-weekend box office for blockbusters, even if they can’t imagine seeing one “Twilight” movie, much less four.

By contrast, TV’s relationship between eyeballs and income is less clear and direct.

Many shows skew older, but the divide is rarely quite as stark as those of “Harry’s Law,” which was NBC’s most-watched drama but had a median viewing age above 60, or CBS’ equally geriatric “Jesse Stone” movies, starring Tom Selleck. Like Selleck’s series “Blue Bloods,” the movies were a hit judged strictly by total audience, but the rating in adults over 50 was nearly 10 times the 18-49 cohort.

Still, canceling “Harry’s Law” and discontinuing the “Jesse Stone” telepic series came as a shock to many fans, to whom the “We love the show but” alibis seem understandably feeble.

Yes, people who work in TV have likely heard why 18-49 reigns supreme: Younger people buy more stuff (fewer empty nesters); will hopefully buy it longer (see actuarial tables); are less brand loyal (not so set in their ways); and are harder to reach (media buyers covet most what they can’t have).

Yet not everybody walks around with all that memorized, and the explanation is hardly obvious, particularly with so many 50-plussers currently supporting their grown kids.

For networks to yank such fare thus becomes the equivalent of a big-box store having a return policy most of its customers can’t fathom. For that matter, failing to detail why the 50-plus crowd is devalued doesn’t endear mainstream newspapers to their mostly-older readerships either.

Nor is the confusion limited to the public. Producers and talent often sound similarly mystified, especially if they deliver a respectable total-audience number that’s discounted for missing the key-demo target.

Reflecting the stance of many in the creative community, Michael Brandman, who produced the eight “Jesse Stone” pics with Selleck, conceded the young-adult imperative has never completely made sense to him. “We both believe with the maturation of the TV audience and the diminution of the numbers in the 18-49 category, (the networks) had better challenge some of these ancient assumptions if they want to survive,” he said.

Some have questioned the system, from CBS research chief David Poltrack to NBC, which tested those waters by coining the term AlphaBoomers to define the baby-boom generation’s oldest segment, which began turning 65 last year.

For the most part, however, the networks have begun touting self-serving new metrics that only cloud the conversation further.

Faced with a 30% year-to-year ratings decline for “American Idol’s” finale, for example, Fox responded by transparently seeking to change the subject, issuing a press release citing how the show established a “social TV” record.

OK, but how many of those posting comments and tweets were twentysomething, left-handed and earn over $100,000 annually?

Barring a shift in priorities, ad-supported TV and consumer media need to develop more convincing shorthand to address these issues — other than blithely ignoring older viewers’ preferences with actions reeking of ageism — lest aging baby boomers start rummaging through closets, looking for their old protest signs.

Being treated like you’re worth less than your kids is already insulting; blatantly being dismissed as plain worthless is that much harder to swallow.