Some applications do not have this type of problem (IE 11, Office 2013, Firefox 22, Chrome 30 ...).
It has nothing to do with ClearType. The font system is correct and that the scaling that has been much improved over Windows 8.1.
Look at the title of CCleaner and buttons are clear.
Config :
Macbook Pro Retina
2880x1880
DPI : 200%
Windows 8.1 Preview