There's no way two normal people would have survived that -- the only reason Peter was able to duck out of the way is because of his spider-sense and Neo-like reflexes, which Doc Ock obviously doesn't know he has. Otherwise, both he and Mary Jane would have been squashed by a flying vehicle, rendering Doc Ock's entire plan pointless. No Peter, no one to find Spider-Man, no tritium.
Was the whole point of the car-throwing stunt to get Peter and Mary Jane's attention (by decapitating them)? Or was that just his way to say "hi"? Maybe Doc Ock was trying to open the window and there were no trash cans around. Of course, the more likely explanation is that they just needed an excuse to shoot a scene with Peter ducking out of the way of a flying vehicle so they could put that in the teaser trailer.
If you look closely, you can see the dollar signs reflecting off Sam Raimi's eyes.
Also, killing Harry's two friends would have only pissed him off (he specifically says, "Don't hurt Peter"), and then he'd never give the tritium to Ock. Why the guy with the huge metal arms didn't just take the tritium in the first place, we'll never know.