White house.gov cost a ton of money to develop for something using open source tools. I think that D6 vs D7 are worlds apart for the average user too. Still relatively complex particularly has extra modules are added. I do credit white house.gov and all the development to bring it forward.
It is successfully used on many commercial sites but most of them are not using strictly open source or in other words they have lots of programming development.
I think Best Buy is another famous site that runs well on drupall. Drupal does have a list of many sites that use the core if you will.