Just read an interesting report on Business Insider that says tablets are about to explode. What they neglect to mention is that the standard web experience is going to shift with it.
The forecasts say tablets will hit 481m units a year by 2015 (that's 3 YEARS away) to put things in perspective there are just over 50m iPads (1&2) sold so far -- so the next 3 years the shape and composition of the e-commerce landscape is going to experience a massive shift.
That's because you can access the web on a tablet, but it's not ideal. Tablets are optimized for apps - not websites. Websites don't slide, drag, drop. They can't access native features on the tablets like the camera and they can't play with other apps installed on the device like facebook, twitter, or pinterest.
We already know that tablet users are much more leisurely, and they hate to read. That means that content ladel SEO friendly sites are going to be out and that web experiences that cater to a more leisurely discovery oriented shopping experience (video?) are most likely going to be the future.
The marketplaces will try to develop their own casual experiences, but ultimately their selections are probably too broad and their relationships with clients too generic to be able to compete with a more nimble focused app built on a Web 5.0 framework.