Well... they pooped in their diaper heavily when Vista and Windows 8 came out, with enormous backlash from users...and they were on the top of the game then, so they could have afforded their cute "innovations". I doubt they want to repeat same mistakes now, with tight market like we have. Even if (when) the "next big thing" comes out, I am sure they will have a strong backward compatibility and "give me my damn desktop back" option.