This is not entirely true. As a professional who has made his own eCommerce site I can say that for most people a professional website will save them tons of time and get better results.

As you mentioned, most storefronts these days can be administrated via a web based portal. So the entrepreneur can still administrate the site even if they use a professional to help get their site setup and working with payment gateway's, shipping carriers, fraud prevention, security, etc...

Regards,
Ben
http://www.lynxsi.ca/