"Really, older people look around for things to spend it on," says Susan Easton, an Indiana University professor who has written extensively in the field of demographics.
Next, "brand loyalty" is not something that lasts a lifetime.
Indeed, women ages 40 to 50 are more likely to abandon a favorite brand than are younger women, according to a 1996 study by Information Resources. In 1997, baby boomers, then moving into their 50s, tried just as many brands of soda, beer, and candy bars as did 18- to 34-year-olds, discovered A.C. Nielsen, which tracks TV viewers' purchases just as its Nielsen cousin tracks viewing habits.
"People are not brand-loyal to the same degree that they once were," says Alan Johnson, director of media services at Mullen, an advertising and marketing communications agency based in Wenham, Mass., whose portfolio includes General Motors. "We live in different times."
Ms. Easton goes so far as to characterize the whole rationale for catering to young adults as a "myth." "It's an idea inside the heads of advertisers," she says.
Companies are willing to pay a premium to sell their products during TV shows that deliver young adult audiences, and so long as that is true, network executives and agencies who sell ad time slots "know they have to cater to this myth," she says.
If it's a myth, it's proving to be a hard one to puncture. The content of prime-time TV shows is increasingly designed to attract the attention of young guys who otherwise would be watching sports (or, worse for advertisers, not watching TV at all).
"They're far more valuable to advertisers than people who watch a lot of television and are regularly available," says Jamie Kellner, CEO of Turner Broadcasting System.
Many experts and critics argue the result is a gradual coarsening of prime time. That's not to say terrific TV programs that appeal to viewers outside this demographic are nonexistent.