Material offered as part of a broader, subject related site is often quite detailed and ambitious.
Many sites simply mix both types of resources.
Education Place has a great deal of information. Those with slower internet connections might not like waiting for each page to load. The editors obviously made a decision that the content and accessibility were worth the delay and most users will agree. The red tabs at the top lead to internet cooperative resources in various academic areas. It's aim is to centralize access to high quality Internet lesson plans, curriculum units and other education resources.