There have been five holders of the title Duke of Clarence and only one has been the eldest son of the Prince of Wales so saying it is a traditional title is a bit of a stretch.
http://experts.about.com/e/d/du/Duke_of_Clarence.htm
The first creation was Lionel of Antwerp - 3rd son of the king (Edward III) - extinct due to no male heirs
The second creation was Thomas of Lancaster - 2nd son of Henry IV - extinct due to no male heirs
Next was George Plantaganet - brother of Edward IV - forfeit on his conviction for treason
Next was George III third son - William IV - merged with the crown
Finally Albert Victor - eldest son of Prince of Wales - extinct due to no male heirs
Like the title Duke of York it has never passed to a second generation through either no male heirs, merging with the crown, or forfeiture. Interesting!!