I would say it's pretty simple; the current approach that AP2 takes isn't the approach that Tesla have been working on for the past (however many) years.
The missing piece here is HD maps.
Until the HD maps are ready, the cars will blindly drive themselves into central dividers, go crazy when the lane lines disappear, take sharp corners at 80mph, decide they love driving into trucks, and generally behave like they're on the sauce.
Be very careful and exercise caution at all times.
The Tesla guys (and all people working on FSD) don't spend their time trying to write algorithms that will slow you down into curves based on computer vision (what the car 'sees' through it's camera system). Why would you? Once the maps are in place, it'll know about that curve way before you get to it, and will know exactly when to slow you down. Same for intersections, roundabouts, on-ramps, off-ramps... anything really. The car will know what to do because it's seen it way before it gets there. The cameras will just be used for localisation within the map itself, detecting and compensating for other vehicles and objects, updating the maps, and checking the path is drivable (i.e "don't crash into stuff")
TomTom, Here, Navigon, Garmin, Google etc etc - I'm sure they're all working as fast as they possibly can to get the HD maps ready. It's a key piece of the puzzle, and one that Tesla probably assumed would be ready in time for when AP2 would *really* be switched on. Until then, the best case is that you get AP1 functionality, which they're getting to surprisingly quickly considering they probably only started it in August!
TomTom Automotive - The future of driving, now
Basically, if you're using AP2 (or AP1), be careful for now... the whole follow-the-lines-and-the-car-in-front approach is
very basic - Tesla are only doing this as a stop-gap to appease HW2 customers who want HW1 functionality. Once the maps and path planning are in place, then you'll see the AP2 system rocket ahead - not just because the HW2 cars have more cameras - but because they have the GPU processing on board that can handle the maps.
So, when people say "how on earth are they going to get to EAP or FSD by 2018?"... Well, it's simple,
they switch on the maps. Dancing lane lines? Doesn't matter - the display will show you the HD map lanes populated with cars the camera has seen. Crazy 'pull to the right'... doesn't matter... it won't do this once it knows the road. Doesn't work in the sun? Well - as long as the radar sees the cars, and can sort-of confirm with vision, it'll be fine.
tl;dr - it'll be fine. Just wait for the maps.