Next time you watch the movie, take a careful look at this scene. Anakin falls off the hovercar before Zam crashes it into the ground. He falls about 5 to 10 metres to the pedestrian street below, which to most normal people is enough to break several bones, if not be fatal. But then watch how he lands. His trajectory is almost completely horizontal. He does a roll as he hits the ground and then crashes, sideways, into a convenient pile of cardboard boxes - perfect for absorbing impacts as every Hollywod stunt person knows.

So, obviously what's happened here is that the gravity field generators have made Anakin's vertical fall perfectly safe - but they haven't done anything at all about his horizontal momentum, which is considerable since he just fell off a speeding hovercar. The vertical fall is not going to kill him, it's the horizontal speed when he hits a brick wall. So it's indeed fortunate that that pile of boxes was there for him to roll into after he landed, rather than simply for him to fall into from above, otherwise he could have been very seriously hurt.

Who says the producers of this movie didn't think everything through logically?

Transcript

{Anakin falls off Zam's burning hovercar and rolls to a stop in some boxes}
{The hovercar crash-lands}
[SFX]: CRASH!!!
{Zam extracts herself from the burning wreck and runs away. Chase ensues}
GM: The assassin flees into a bar.
Anakin: Oh good. I need to pick up a new laser sword.
Anakin: Hopefully before master Obi-Wan finds out I dropped mine.
Obi-Wan: {appearing, after having landed the other hovercar} Or I could just sell you this one.