You need only look as far as its
Internet Explorer Test Drive site to see how the company feels about HTML5, so it shouldn’t surprise anyone that Flash is playing a diminished role Windows 8.
As far as I've understood this restriction will be only for the touch version of Internet Explorer 10,however with HTML5 getting developer day by day,one thing is sure...... Flash has its days counted......
Without a doubt this will be at first a pain in the *** for the webmaster however,on the long term this is very beneficial for the end user.