I don't consider that quip anti-scientific at all. I take it as a reminder that you must always test your theories against reality, because the ways that reality and theory differ might be greater than you realized.
To address your original question, the realities of controlling an actual car are probably the hard problems. Dealing with things such as the inertia of the car and tires slipping on the road are probably both required to solve the problem, and difficult to simulate accurately. Simulations only simulate what we know about. It's often the things we didn't anticipate that make the difference between success and failure.
I'm sure it never occurred to anyone on these teams to try out their code in a simulated environment. I'm 100% positive their development model was to crash car after car after car until they got it working. I can only imagine how expensive some of those bug hunts got.
ya, srsly. From what I've seen they are hacking together the hardware and then constantly updating the code to get just barely working solutions, oftentimes in the middle of the testing. If some teams are running a fairly complex car physics simulator with simulated input from each of the types of sensors they are using this would be the first I've heard of it.
that presumes an unreasonable amount of homogeneity in both the programming languages of the entrants and the sensor platforms of their vehicles. The entrants may very well do that inhouse for testing purposes, but since Darpa is merely responsible running the competition and determining if the prize award is merited, why on earth would they do something that would unduly constrain the entrants?
To address your original question, the realities of controlling an actual car are probably the hard problems. Dealing with things such as the inertia of the car and tires slipping on the road are probably both required to solve the problem, and difficult to simulate accurately. Simulations only simulate what we know about. It's often the things we didn't anticipate that make the difference between success and failure.