Windows gets exploits too, but that doesn't mean it'd be a good idea to replace it with Chrome OS and lose all the software that doesn't exist out of Windows.
Why 90 days? Why not 30, 14, or 7?
Microsoft might have requested responsible disclosure for exploits affecting Windows, but what gave Google the right to set a deadline?
I feel the 2 US companies have a friendly competition with each other which can help secure their systems.