Quote Originally Posted by Trailer Park Ninja
I know this is the G1 fan in me when I just hated the idea of Megatron answering to someone else, even to the point he would bend down on knee in servitude.
The RotF prequel explains Megatron's subservience to the Fallen. Also, Megatron did take orders from others in G1, such as Lord Straxus and Shockwave.

"Hail Shockwave, Decepticon Commander Supreme. I function for you and you alone." - Megatron (The Worse of Two Evils)