My suspicion is that they are way ahead of competitors in terms of data from testing self driving cars and realize there are still so many unsolved problems that true autonomous vehicles aren't going to happen nearly as soon as competitors claim.
For instance, I see self-driving Google cars on a daily basis here in central Austin. There are a ton of zero visibility turns where you have to slowly edge out and hope no one is coming because visibility is blocked by a hedge.
How can self-driving cars handle that scenario without delegating to manual intervention?