Vision is probablistic. You can improve your probabilities with more data and deeper nets, but the probability is never 100%. Inferring depth using triangulation of extracted features using vision is also probabilistic.
Lidar gives you very rudimentary depth and positional data, but it is precise, and reliable, and the false positives are low. Lidar is not seeing the world as a series of probabilistic phantasms that may or may not be a pedestrian, or a jersey barrier, or whatever.
Elon said: "Lidar is lame! Lidar is Lame! lame lame lame lame."
But then he later said: "We've gone over this multiple times. Are we sure we have the right sensor suite? Are we sure we have everything we need?.... No."
Lidar is a crutch and we'll see how hard Tesla is limping in a couple years when Elon is claiming They're going to have Robotaxis.
To Tesla's credit, it is theoretically possible to develop a fully autonomous vehicle without needing Lidar, but before you can deploy, you need to integrate Lidar, and it can be retrofitted as a largely independent system, necessary for it's enhanced redundancy, but not needed for informing the planner, except when the Lidar is seeing things the vision system isn't.
The presentation was a pretty good run down on various techniques and methods that are being utilized by different autonomy developers. The downside is that everything is framed as a rationalization as to why Tesla has some kind of secret weapon, when they're mostly doing conventional things, and not all the conventional things you need to build a complete autonomous vehicle.
I was waiting for Elon or Karpathy to trot out the magic pixie dust that will have Tesla's driving empty in a couple years, but that was nowhere to be found.