In The Outsiders, why does Ponyboy remind Cherry that they both watch the same sunsets?

Ponyboys wants to tell Cherry that they're not so different.  He may live on "the wrong side of the tracks" and she may be a rich Soc, but they're both teenagers who see the same sunset.  They live in the same town and are separated by social class, but Ponyboys wants her to know that that in itself doesn't make them totally different. 

On the way home from the movies at the Nightly Double, Pony and Cherry talk a lot and reveal things about themselves that they probably never would have imagined telling a "Soc" or a "greaser" in another situation.  They realized how much they had in common, but as soon as Bob pulled up, things had to go back to the way they'd been before.

Later in the book, Pony reminds Cherry that they both see the same sunset.