Angle/libEGL uses (in Surface.cpp) the following DWM functions that are only available on Windows Vista and later.
The Windows platform plugin links to libEGL, which in turn currently hard-links to DWMAPI that does not exist on Windows XP. This causes that Qt5 applications currently cannot be run on Windows XP. In order to support Windows XP, dwmapi.dll must be delay loaded.
The original libEGL.vcxproj does it like this: http://code.google.com/p/angleproject/source/browse/trunk/src/libEGL/libEGL.vcxproj#172.