On a system running Windows 8, the Desktop Graphics component of the system's Windows Experience Index may appear to be slightly lower than what is reported in Windows 7.
In Windows 8, the assessment to determine a system's Desktop Graphics score was updated to include an alpha blending workload. This improvement to the Desktop Graphics assessment may result in a slightly lower Desktop Graphics score than what is reported in Windows 7 (a 0.1 to 0.6 point reduction).
This behavior is by design due to improvements made to determine the display’s adapter Desktop Graphics performance with better accuracy. The score can be compared to other systems running Windows 8, as other Windows 8 systems will undergo the same alpha blending workload during the assessment.
Your Desktop Graphics score can be viewed by going to Control Panel > System and Security > System > Windows Experience Index.
Desktop Graphics assessment