Are those approaches mutually incompatible? It seems to me that it would be easier to build a system which can drive fast when what it's seeing matches what it's expecting to see (most of the time), and which falls back to a much more conservative stance in the case of surprisal (i.e. expectation not matching observation).

If all the cars are always mapping and collecting data will maps ever be out of date?

Think of all the many times a software developer says "X will never happen."

Then think of what percentage of the time they're right.

Yes. Cast your mind to lightly-traveled rural roads. If you are driving one of the many unpaved roads in Arizona during flash flood season, and the last car through was a couple hours ago, will you bet your life that the road is still there?

But hey, that's not a realistic danger in the city, right? Well, look up the sinkhole named "Steve" that opened up in the middle of an Oakland, CA freeway.

Then there's Highway 1, which is known for landslides. Not to mention that little incident with the Bay Bridge back in '89...

By definition, any car that makes an update to a map has experienced an out of date map.