My take:
God can completely observe everything because of omniscience. He is above uncertainty. This is philosophical.
We cannot directly observe everything because we need to impart some sort of energy to the things we are observing (be it a stream of photons or other energies). At the smallest known levels, we can't even observe matter as matter, but must observe it as waves.
I would say that we cannot observe all matter completely since much is only observed by it's interaction with other things, which (if dealing with only our senses) is like observing what the wind does, even though we can't see the wind itself.
Joe
the neophyte, non-formally educated, neo-wannabe-quantum-physicist in training!