That is true but that is not the point of the movie or what Spielberg and Kushner were trying to convey: the legal eradication of slavery (as opposed to self-emancipation, which had been going on for some time). Some have complained that they should have mentioned Frederick Douglass but, again, how would he have fit into the story.
Regarding Django, some have grouped the movies together because how both portray slavery and Django has gotten high marks for that. However, in other ways -- use of the "n" word and slaves getting revenge on masters -- it has come in for criticism. Most slaves were not interested in revenge but having the chance to have their own lives as they wished.
I would expect Django to do better at the box office because it's Tarantino and there's more action. However, in the US, Lincoln has approximately $176 million vs $154 for Django. Overseas, it's different, primarily for the reasons I mentioned: Django has $187 million vs. $47 for Lincoln.
