1cm? OMG?!!
Ok. I can see that for construction, some survey applications (volcano's for one) and to see how much Galloping Gurdie is moving before having to evacuate the place.
Navigation though? That's serious overkill in a big way. Without support I can just barely hold a receiver to those limits when standing up in a steady very light breeze if I'm really careful... But I should be able to get to a location and when it says "arrived", slide my key into the slot in the door knob without a funnel or additional guidance.
Not getting lost, or getting unlost after getting lost, I can see that. But 1cm for navigation, while it's technically possible, is in the realm of excessive overkill in the real world.
I often wonder about that. We're already in the close enough that it really doesn't make any difference category until they shut down or seriously degrade the system for security reasons. WAAS is good for what? 3 meters give or take a meter? Off the shelf $100-$150 GPS WAAS systems commonly have accuracy to 20ft and 30ft is almost a given. They may not be able to put a missile through a small bathroom window with it, but 1000lbs of high explosive traveling at 500mph with 3-10m accuracy is still going to be able to wipe out unhardened targets even considering stacked tolerance errors. Same goes for someone walking up and setting a suitcase down at a given location and walking away.