Why are Johnny and Two-Bit surprised that Ponyboy does not always get along with Darry?

Johnny and Two-Bit don't see things the way Ponyboy does. Ponyboy thinks Darry would like to be rid of him.... his friends know that he's wrong.

Two-Bit and Johnny were staring at me now. "No..." Two-Bit said, dumfounded. "No, Ponyboy, that ain't right... you got it wrong..."
"Gee," Johnny said softly, "I thought you and Darry and Soda got along real well..."