It is clear that J.K. Rowling took extraordinary care in crafting the first book in her Harry Potter series. Therefore, it appears that there must be some significance to the fact that Harry believed that his parents died in a car crash before learning that he was a wizard. In order to understand that significance, it is important to examine how Harry learned that his parents did not die in a car crash. Interestingly enough, no one in the wizarding world revealed the true nature of his parents' death, instead his aunt Petunia exploded about their deaths when Harry was approached by Hogwarts:
"Then she met that Potter at school and they left and got married and had you, and of course I knew you'd be just the same, just as strange, just as – as – abnormal – and then, if you please, she went and got herself blown up and we got landed with you!"
Harry had gone very white. As soon as he found his voice he said, "Blown up? You told me they died in a car crash!"
"CAR CRASH!" roared Hagrid, jumping up so angrily that the Dursleys scuttled back to their corner. "How could a car crash kill Lily an' James Potter? It's an outrage! A scandal! Harry Potter not knowin' his own story when every kid in our world knows his name!" (Rowling, p.53).
From the passage, it is clear that Petunia has a tremendous amount of disdain for wizards in general, and Harry in particular. Therefore, it seems likely that this disdain is at the root of their lies about the method of Lily and James' death. As a result, it is important to understand Petunia's disdain for wizards and wizardry, in order to understand why she lied about the manner of James and Lily's death.
The Dursleys' issues with Harry being a wizard are an important element of foreshadowing. By denying that wizardry had anything to do with the death of his parents', the...