Evan Schuman's StorefrontBacktalk

But the unwillingness of so many big retailers to cater to tablet-using customers is puzzling. Particularly surprising is eBay, which on Monday (Sept. 24) announced it has reached the milestone of 100 million listings via mobile, as well as 100 million downloads of its app. But eBay served up the same mobile site on our test tablet as on a phone.

Is it because chains expect customers to download their apps? That’s not a safe assumption. True, customers can easily install and delete free retailer apps. But that takes time, and just a little bit of commitment that shouldn’t be necessary for a bit of online shopping. Imagine telling in-store customers, “We’ll let you in, but our associates won’t treat you like a first-class customer unless you join our loyalty program.” Again, that’s a great way to drive new customers away (unless you’re Costco or Sam’s Club, in which case you won’t even let them in unless they join).

Do M-Commerce developers assume that it’s enough to have a link to the full-scale site? That they can afford to annoy customers the first time, but once a customer has clicked through to the full-size site it’s enough to remember that so the customer will never see the minimal mobile site again? That is the way many mobile sites and mobile browsers work. But because the mobile versions of most chains’ sites begin with “m.” or “mobile.” it’s easy enough for customers to find the minimal site. Why risk annoying the customer at all?

Or maybe most chains figure it’s safer to lump tablets in with phones than with PCs. That may be exactly the wrong way to split the market.

After all, those minimal mobile sites have always been a pretty terrible compromise. The list-o’-links design approach makes it possible for users to click on a tiny touchscreen, but that’s all. No marketer would choose to serve up such simplified sites, on which almost no products are on display and where it’s impractical to highlight most promotions. (Need proof? Those are exactly the things your marketing people stuff your full-size homepage with: promotions and pictures of products.)

That means getting away from minimal sites is exactly what M-Commerce developers should be doing, and not just for tablet users. Phone screens are steadily getting bigger—with each passing month, a random M-Commerce customer’s phone is more likely to be able to handle a full-size site. Meanwhile, half of customers in the U.S. and western Europe are already using smartphones, and much of that growth is at the low end, with users trading up from feature phones.

So while new smartphone users are flowing into traditional, minimal M-Commerce sites at the low end, high-end phones are ready to leave minimal sites behind, and tablets are already there. In short, the split between “mobile” and “regular” Web sites is no longer lined up with mobile devices vs. PCs. It’s all about screen size—and, increasingly, M-Commerce will involve big screens for customers with the most money to spend.

Eventually that will mean doing the little extra work necessary to identify tablet and big-screen phone users. Serving them an appropriate Web site will then become the standard.

In the meantime, it looks like an instant advantage for almost any chain that does it.