Having read the book since watching the film, I have to agree with previous posters. The film completely misses the point of the book, and thus the title is pointless.
Just to reiterate, at the end of the book, Neville realises that civilisation has moved on without him, and the vampires are now the social norm. As they are only just developing the ability to go outdoors in sunshine, Neville has been massacring them during daylight hours. In the final act of the book, he accepts that they are now going to kill him, but is surprised to see that the vampire population is scared of him. He has become the "creature of the night" that vampires used to be. He is legend.
Will Smith wasn't. In the happy Hollywood ending, the zompires didn't become the new civilisation.