Skinny people only, please. (Mary Altaffer/AP)

It hasn't been a good couple of weeks for fashion brands that don't want bigger people wearing their clothes. Abercrombie & Fitch, whose longtime CEO Mike Jeffries insisted would only market to "cool, good-looking kids," finally decided to offer larger sizes after its declining popularity became too dramatic to ignore. And the pricey workout wear company Lululemon got dinged when its founder suggested that some women were just too big for its yoga pants, for which he later apologized.

Public opprobium isn't the only reason those remarks were regrettable. Insulting larger customers is also a terrible business decision, given the ever-increasing American waistline; more than a third of Americans now qualify as obese. Clothing companies have known this for a long time: Liz Claiborne launched a plus-size (or "special sized," in industry parlance) clothing line in 1989, and higher-end retailers kept moving into the category through the 1990s. Even Hot Topic was hip to the trend in 2001, accommodating the needs of pudgy goths.

At the same time, though, it's not always easy to incorporate larger sizes into floor displays. They require bigger mannequins, which can be costly to procure; the British department store Debenhams' just debuted a set of figurines to represent size 16. Retailers say that larger people are less uniform in shape; you can't just take the measurements from a size 6 and multiply by three to get a size 18 that would fit well.

Weightier women find shopping more stressful than slim ones, and often prefer to buy clothes online, which further disincentivizes stocking plus sizes in stores — Old Navy and Ann Taylor have moved them all online, and while Forever21 and H&M also have plus-size Web pages hidden on their site, their mass advertising skews skinny. Finally, obesity also tracks with poverty, making overweight people in the aggregate less valuable customers than skinny people (which isn't to say there's not strong demand).

"Most retailers can't afford to fit everybody," a National Retail Federation official told the AP last month.

So it's not actually shocking that even after all these years, Abercrombie and Lululemon — which only offers women's sizes up to 12 — aren't that far outside the norm for mainstream retailers. According to the NPD Group, sizes above 14 only account for 10 percent of sales, or $14.56 billion over the past year, which has hardly budged as a percentage of the overall market. It's just that most company CEOs don't talk about not wanting to make clothes for fat people in public.

Plus sizes beat teeny yoga pants, by stock prices at least. (Yahoo)

Clearly, though, it's possible to make money serving the full-figured (even Spanx is getting into jeans!). Lane Bryant, arguably the nation's most recognizable exclusively plus-size retailer, has been aggressively expanding in recent years. Its parent company, Charming Shoppes, was purchased by Ascena Retail Group last year, and it's been doing much better than its super-trim competitors.

Retailers that don't have to market plus sizes next to the more "aspirational" fits could just be the ones to scoop up the market.

How Ascena positions Lane Bryant. (Ascena Investor Day presentation)