They are careful to state that you should always keep your hands on the wheel. There's even a little popup on the instrument panel that says this when you engage the system. But they don't enforce it.
Google had an enormous technology lead but they've squandered it on a clowncar that remains a concept. They're overthinking the product, how can we ensure people aren't afraid of the technology? Make it cute. Riiight. Funny how they don't mention any pre-orders.
Shipping autopilot was bold and smart. Tesla has a deterministic path forward. Meanwhile Google and the traditional car companies are lost in indecision. And Apple is starting out even further behind. Tesla's autopilot is a wake-up call for all of them.
EDIT: Qworg, they can add a sensor to the cars they ship at any time. They did it in the past and you can be sure they are doing it now. The others still need to figure out how to ship a single car.
I'm not sure GoogleX had to approach self-driving as a product. At least, not until Alphabet.
Tesla's implementation is the best out there, but it's not substantially different from what you'll find on a high-end Infiniti or Volvo or Mercedes today.
80% of the benefit of Autopilot is the traffic-aware cruise control. That's basically just a radar unit that keeps you from hitting the car in front. Remarkably useful, but not anything like a phase change.
If and when true autonomous technology arrives, that certainly will be a phase change. And Autopilot is a step (a small one) in that direction. But it is not by itself a prticularly big deal.
(Full disclosure: I've driven maybe 1,000 miles with Autopilot, and a few thousand miles with the pre-Autopilot traffic-aware cruise control.)