DirectX is a patch because of a bugger up Microsoft made in Windows 95 ... if they charged for it there is a large chance most of the industry would boycott the Windows Operating System.
Believe it or not OpenGL just isn't stable enough to take the Graphical Place of DirectX - remember it isn't just a basic Graphics APi, but is within every single Driver ... but is a Generic Driver.
So the simple answer is, no you won't owe Microsoft Money - its like using the Windows OS, you're not charged per usage - only a one time fee for access to it
Tsu'va Oni Ni Jyuuko Fiori Sei Tau!
One block follows the suit ... the whole suit of blocks is the path ... what have you found?