Off topic, I think that is one of the best scenes of Megatron.

 

I have noticed this for quite some time.

 

Yeah I saw that too the very first time I saw it in theaters.

 

It had no face, therefore, presented no reason to be a.) saved or b.) attacked.  

But seriously, I get what you're saying, I mean, there are humans in there! Save them, Optimus! But I honestly don't think that doing such a thing would've been easy, even for Optimus. You've got a 30 foot piece of metal with GIANT SPINNING BLADES careening out of control. Even attempting to stop it/slow it's descent would've probably killed the pilots (if they weren't dead already), not to mention injuring Optimus himself. It'd be like if Edward Scissorhands was riding a bicycle towards you at 15 kmh with no control over it and flailing his bladed hands around and you had to try and step in front of him to stop him. Not that easy, huh?

Yeah, really only a couple of lines in each movie. Around 4 in the first movie, 10 in RotF and 4-ish in DotM. Again, all in wide battle shots.

 

Optimus barely has his mouthplate on, but when it is on, it moves when he talks.