Amazon.com Inc. may be ready to close up shop on Endless.com, the web-only shoe and handbag store it launched in 2007, according to a tweet today from Peter Cobb, co-founder and senior vice president of marketing for eBags Inc., a competitor that sells handbags, backpacks and related products. “Per reliable source, Amazon shutting down Endless.com soon. Shows how difficult it is to build an enduring brand,” he wrote.

Cobb declines to elaborate on his Twitter message. Amazon did not respond to requests for comment.

Amazon.com, No. 1 in the Internet Retailer Top 500 Guide, also owns Zappos.com, which it acquired in 2009, and Zappos.com sister site 6pm.com. Consumers also can buy shoes on Amazon.com.

Housing four distinct shoe sites under the Amazon umbrella seems excessive, says Scot Wingo, CEO of ChannelAdvisor Corp., a company that helps retailers sell through online marketplaces. But the arrangement enables Amazon to add “shelf space” on natural search results for products sold by the e-retailer, he says. For instance, a Google Inc. search for “Asics Gel Nimbus 12,” a type of running shoe, returns five natural search results for pages on Amazon-owned sites.

Having more ways shoppers can buy likely added incremental income to Amazon’s bottom line at little incremental cost, says Colin Sebastian, an analyst who follows e-commerce stocks for Lazard Capital Markets.

“Amazon really is a technology company,” he says. “They probably were getting a stream of data from Endless.com that they considered useful. That might be attracting customer segments that are different from the core Amazon site or Zappos. And the incremental cost to maintain a separate site is probably not that high. While it appears to be a stand-alone site on the consumer end, it was probably well integrated on the back end with Amazon.”

If Amazon does shutter Endless.com, it will be because the incremental cost of maintaining the site exceeds the additional revenue the site generates, says Sebastian. “Amazon is always experimenting,” he says. “They’re a flexible oven. They try a lot of different things—some of which work and some that don’t.”