Hello Jitendra
I'm not quite sure that what you wrote about Microsoft's standard display driver not being signed by Intel was correct.
All hardware manufacturers who want to prove that their devices are compatible with Microsoft OSes are encouraged to obtain WHQL certification. As Microsoft does not manufacture display adapters for desktop monitors, why would it want to seek WHQL certification?
Did you know that Intel does not provide drivers when Microsoft's ones perform the same job equally well?
Let me give you an example.
Despite repeated requests from about 100+ customers of Microsoft Windows 8 and 8.1, Intel has flatly refused to offer its own USB 3.0 native driver. It gives the excuse that the generic USB 3.0 driver provided by Microsoft works just as well. Intel only provides its own USB 3.0 driver for Microsoft Windows Vista and 7 customers.
Customers of Microsoft Windows 8 and 8.1 will tell you that the generic driver provided by Microsoft does not provide the full bandwidth performance expected of a USB 3.0 device. But Intel does not seem to care.