Also, define additional "optional" gameplay content. What if they had cut Gaurrus from the game and made him playable via a $10 DLC, the game would still be beatable without him, so would that be fine? What about if they cut out something like a higher difficulty? Ect.
It was made before the game was released, it is a character who is integral to the story (being a prothean and all) and it would not be given out for free as they would have made their money from it because of the game's sales.
And who said anyone has to work for free? EA/Bioware are making money from the game's sales and they are paying their employees. No one is working for free there. The cost of developing the DLC could have be factored in earlier when they started development. "Hey, we're going to have some downtime after the game goes gold, let's put aside $X to go towards some additional DLC for release day so that we aren't sitting around doing nothing or getting laid off." No one working for free in the scenario.