Is "clearing" a shopping cart with one button still as important as it use to be? My first thought is no, especially since it is very common to have a "remove item" link next to the product. However as I think about it now I might change my mind.
I believe that there are somethings on a website, especially for online stores, that are needed to portray a sence of security and trustworthiness to the user. The "clear all", "clear shopping cart", and "remove all items in cart" maybe one of these feel good items. Plus (I would need some real feed back here) I bet assistive technology users would like to have "clear all".