Up until now in Windows 8 and Windows RT, the Metro version of Internet Explorer 10 would only run flash on websites that were whitelisted in the Internet Explorer Compatibility View list. Even though you could add websites to the whitelist (I even made a script for it), most people didn’t knew it or just aren’t that handy with computers to fix this themselves. This ofcourse leads to a bad user experience.
Now Microsoft has decided to allow all flash websites and only blacklist some that don’t meet the standard (apparently less than 4% of the tested websites). You can read more about it here: http://blogs.msdn.com/b/ie/archive/2013/03/11/flash-in-windows-8.aspx
I think this is a good move, because it gives an advantage over other tablets. I think this should’ve been this way from the start, but better late than never.