Long time ago Microsoft has announced that they are working with Adobe to integrate Flash into IE 10 so that it can run flash contents without installing external flash plugin. Google Chrome already comes with such feature in which you dont need to install anything as it comes with its own flash player.
Now Microsoft is going to release a patch through Windows Update for IE10 for Windows 8 and RT which enable flash for default on IE 10. This change comes because the vast majority of sites with Flash content are now compatible with the Windows experience for touch, performance, and battery life.
You have to note that it will affect only Metro Version of IE 10 not desktop version in Windows 8 or Windows 8 Pro, for that you still needs to install flash separately.