Just like how Apple has refreshes the iTunes logo recently, Microsoft has done the same with their upcoming Internet Explorer 9. Microsoft is aiming for a lighter weight and fresh modern look of Internet Explorer 9.
From Microsoft blog:
To reflect this in the logo, we focused on revealing only what is essential, reducing ornamentation that might call undue attention to the logo itself. To indicate speed and fluidity we applied more subtle shading and bevels than the IE 8 logo. The effect is an overall flatter and more lightweight appearance. To stay true to the Windows 7 aesthetic, we chose fresh colors and shades to complement the Windows 7 color schemes that IE9 is built on.