Hierarchy of information
The other problem is the amount of unnecessary information on the screen. In good interface design, superfluous information should be hidden or at least depreciated in emphasis by 'greying-out'. It is not necessary, or desirable, to offer every option at every step. It might make things easier for the designer to have a constant navbar on every page, but the word 'design' suggests that the object of the exercise is to make things easier for the user.
Again, the use of off-the-shelf shopping cart programs makes things easy for the designer but if the shell scripting means that the end result is difficult to navigate and use by the customer, then it is a bad design choice.
E-commerce is going to happen. Big! But like any store on any street, success will depend on customer satisfaction and loyalty.
The Web site presentation replaces the store front facade.
The way the products are presented on the site replaces the in-store displays.
The text on the Web pages replaces the sales people.