Like most others I found the Megatron/Starscream chat to be great but there is something I don't get.

Spoilers:

The convo between Megs & Starscream was long overdue, but what I don't understand is to me it felt like Megatron needed Starscream on his side purely to get the Decepticons into action, as if Megs was unable to do it himself, which to me made no sense. Right after their little chat Starscream was the one who gave all the orders and Megatron is unseen until Roadbuster puts Astrotrain through the wall and lands near him.
What is Megatron doing in this time ?
And why is Starscream giving out the orders ?, Is Megatron's commlink busted or something ?