Check out this new article Wizards of the Coast posted recently:

Blog: The Role of Skills

Skills have their origins in nonweapon proficiencies from 1E/2E and the percentile-based skills from the thief class. In 3E, a skills system based on spending points and increasing ranks gave universal access to skills to all classes, and 4E took the concept and made some changes, with a binary trained/untrained choice and a streamlined skills list.