Evan Schuman's StorefrontBacktalk

After two years and 125 million iPads and other tablet computers shipped, most large chains’ mobile Web sites still don’t seem to know that tablets exist. They still serve up an M-Commerce site designed for a tiny smartphone screen, which looks somewhere between mediocre and terrible on a tablet screen that’s seven inches or larger.

That means just a few years after chains finally figured out the importance of customizing M-Commerce sites for phones, there’s a new advantage to be gained by spotting which mobile devices don’t have tiny screens and giving them their own customized tablet sites—or at least the full-size Web site.

Among the largest retailers, only the Amazon, Home Depot, McDonald’s, Kohl’s, Apple, JCPenney, Gap and Overstock Web sites showed up in a tablet or full-screen version. Staples.com showed up on a seven-inch tablet with slightly more content added to what was still clearly a site designed for a phone screen.

But Walmart, Target, Walgreen, CVS, Lowe’s, Best Buy, Sears, Macy’s, Rite Aid, TJ Maxx, Nordstrom and even eBay served up exactly the same screen for a tablet as for a phone with a screen a small fraction of the size. On the phone, those compact, minimalist sites help usability. On even a small tablet, the result is vast expanses of blank space that all but drives away customers.

This wasn’t what we were expecting when we started looking at how E-Commerce sites show up on a tablet. Tablets certainly aren’t new, we figured. The installed base of tablets is about 125 million as of June 2012, according to industry parts-watcher iSuppli, and that number is roughly doubling every year. They’re very, very much on the minds of retail IT shops for in-store use. Of course big chains would already have tailored their M-Commerce sites to handle big screens well, just like everyone finally launched mobile versions of their sites to handle small phone screens. Or so we assumed.

Not so, it turned out. The only accommodation most chains have made to tablets is that there’s a link at the bottom of the mobile homepage to let shoppers see the regular E-Commerce Web site.

That sends a clear message: “We can’t bother to notice you’re using a tablet with a screen big enough that it makes our mobile site look silly or ugly or both. But if you really want to see a full-size site, we’ll allow you to scroll to the bottom of the page hunting for a link to click.” Yeah, that sure won’t drive customers into the arms of competitors.

Of course, not many competitors are identifying tablets as different from mobile phones. The ones that do mostly seem to serve up the standard full-screen E-Commerce site for tablets and a typical phone site for phones, though there are some interesting variations.

For example, Staples did show a few more links at the top and bottom of the screen when we tested it with an Android tablet, compared with what showed up on an iPhone screen. It was still basically the same mobile site, and it wasn’t clear whether the difference was tablet-vs.-phone or Android-vs.-iPhone.

Apple’s mobile site, on the other hand, looked almost exactly like its regular Web site, except that on the tablet it rearranged itself when the orientation changed from portrait to landscape. Interestingly, on the iPhone it correctly identified that it was an iPhone and served up a slightly different site—more links, a special version of the iPhone 5 image that dominated the homepage. But even after correctly IDing the phone, it didn’t adjust the page to make it more small-screen-friendly. (Maybe Apple is hinting that it’s time to buy a phone with a bigger screen.)