While we're on the topic of static H values, I know why programs keep being written that think InvalidateRect(NULL, ...) refreshes the desktop.
HWND_DESKTOP is defined as 0.
Yes I know it's only for CreateWindow & friends, but it's not immediately obvious to someone who sees the definitions but not the documents, so the do InvalidateRect(HWND_DESKTOP, ...) and expect everything to be repainted.