One Thing That I Think Tolkien Did Wrong and Jackson Did Right

[Boromir88]

I fail to see how the movies got this one right when movies are notorious for hyping up the large battle sequences and getting physics and reality wrong (but that's also part of the appeal to movies). And your other evidence is a faulty drawing of catapult trajectories.

And on another note:

Originally Posted by TheAzn

As you have already known, 40,000 Mordorians is a very conservative number; heck even 80,000 is still considered to be a moderately conservative number. With this in mind, the Mordorians/Morgulians/Haradrims/etc. would have to be far closer to Minas Tirith than 7 miles.

Well, 40,000 is the the low ball estimate, but 80,000 is at the very high end. The estimate for the Pelennor Fields is really 40-65 thousand. Sauron's force coming out of the Black Gate was 70,000 and I haven't seen a case to show his combined Pelennor Fields force would be greater. The movies 250,000 or whatever it was was again, the film business liking the large, epic battles.

[Galadriel55]

There is also this point which was mentioned before but not really elaborated on: the Mordor forces were firing heads over the walls of the first couple levels, and some small loads that would explode into fire. Gondorians were most likely firing large blocks such as you see in the movie. A catapult shoots lighter loads much farther than heavier loads. Gondor did not, for a fact, have anything that would equal to Mordor's explosive loads, and what's the point of firing heads at the orcs?

As for the preparation Denethor would have done, remember that Minas Tirith is unassailable. You can't break the walls with catapults. The Gondorians laughed at Sauron's catapults, because they would not do much harm to the walls. Denethor does not need to prepare a defence for a catapult attack, he has one already.

ETA: and yes, as Mumriken said, height could give advantage to, for example, archers, who shoot on a much flatter parabola. But not so much catapults.