It would only make perfect sense that Ashlee Simpson’s success and the success of her MTV show stem mainly from her teen fans. She is indeed so teeny. There was her stint on “7th Heaven,” her appearances on “TRL” and the fact that she herself just turned 20 in October. She's several years younger than big sis Jessica.

But it's simply not the case.
   Season two of MTV’s “The Ashlee Simpson Show” debuted last week, and it turns out the singer is hot with just about everyone but viewers 12-17. They are not watching in droves.
   "Ashlee" ranked No. 4 for the week in MTV’s target 12-34 audience, attracting 2.07 million viewers. That put it right behind its lead-in, sister Jessica’s “Newlyweds,” whose season premiere brought in 2.4 million.

Similarly, among viewers 12-24, “Ashlee” finished No. 5 on cable last week (1.33 million), right behind “Newlyweds’” No. 3 finish (1.58 million).

Yet among 12-17s, it’s quite a different story. The “Newlyweds” premiere finished No. 8 among teens, bringing in 653,000 viewers. But “Ashlee” lost 21.2 percent of that demo, pulling in 514,000 12-17s and not even cracking the top 20.

One almost hesitates to ponder why teens adore Jessica but have chilled on Ashlee. Maybe Ashlee’s teen fans are still upset about the whole “Saturday Night Live” lip-syncing fiasco. Maybe they prefer a little more conflict in their reality fare a la “The Real World” or the oft-bickering “Newlyweds.” Or maybe seeing Ashlee booed off the stage at the Orange Bowl was taken as a signal that the younger sister is about to become yesterday's pop news.

But actually, it turns out teens never particularly cared much for Ashlee in the first place.
   Back in July, during the first season of her show, all four episodes of “Ashlee” made the top 20 for the entire month on cable among viewers 12-34. Not one of those episodes made the top 20 among teens.

In August, the lone episode of “Ashlee” that aired finished the month in the top 10 on cable among viewers 18-34 but failed to show up in the top 20 among 12-17s.
   Is there deeper meaning to be read into all of this?

Certainly some. It suggests that the younger sister's career isn't as promising as it appeared in the summer when her show showed steady gains on her older sister's. If you're a dud with teens and you're on MTV, you've got a problem.
 

It also suggests that even the star-creating machine that is MTV has its limits, and passing the less-talented Ashlee off as a singer may be one of them. Having seen her star rise over the summer, might we now see it flutter, flicker, fumble and fall in these dark winter months? Worse destinies have befallen finer talents.
 

Elsewhere among young viewers, Fox’s “American Idol” was dominant in just about every demo last week, its second of the season. Two episodes of “Idol” finished Nos. 1 and 2 on all of broadcast and cable in every demo—total viewers, 18-49s, 18-34s, 18-24s, 12-24s, 12-17s and 9-14s—except one, 2-11s, in which it finished No. 1 and No. 3.
 

In that demo, an episode of Nickelodeon’s “SpongeBob SquarePants” snuck into the No. 2 spot, attracting 2.88 million kids 2-11.