I'm not sure Optimus doesn't use the magma lava swords of doom at the end of the first movie. Most of the fight with Megatron is left out of the finished film. There are some weird things about it too. Like where did Megatron's leg go? He's missing a whole leg and an arm when they dump him in the ocean at the end! You can clearly see he still has that arm when he dies in the city. I don't know.