It's Star Wars.
You can say this, but its not the days when Star Wars as a concept, was the biggest game in sci-fi / fantasy filmmaking. Since the 2000s, a large number of fantasy films completely surpassed Star Wars as a top movie interest, and that was due to more than the prequels being terrible.
Many people went to see Avatar just to see the revolutionary 3D. You had people who didn't normally go to genre films, or movies in generally, lining up to see Avatar. My wife saw it four times because she kept taking friends who wanted to see the 3D.
The story itself was secondary, although it certainly helped that it was engaging and accessible.
TFA is going to make a lot of money, but for it to beat Avatar it will need to be a quality, engaging story that people can take both their children and their parents to go see.