It's a great idea in theory, the problem is that corporate designs go through ten different committees each wanting something different, so you end up with an unusable mess.
http://theoatmeal.com/comics/design_hell - How a Web Design Goes Straight to Hell
From my experience, getting feedback from a small team in 20 person startup can drastically change the site from the designers original vision.
At the bigs companies there are many different stakeholders who need to be appeased. Some of the changes may seem illogical to the average consumer, but they might be well justified by management. For example trying to keep a few big corporate clients happy by including a large cheesy marketing message on the homepage.
Edit: But I admit, DHL is in desperate need for a redesign. Their website is awful.