I think of it as like Charmeleon was like a teenager. It had paid attention to Ash when it was young and naive, because it Ash showed it caring and love. However, when it got older, and learned more, it became cocky and saw Ash for what he was-- a rookie trainer that was still learning many of the basics. I think Charmeleon felt as if he didn't have any respect for Ash. When he started listening to Ash in the Orange Islands, it was after he saw how dedicated and serious Ash could be, even to something that was repeatedly rude and menacing to him. I think that when Charizard saw Ash doing that, he began to have some respect and admiration for the boy.
Charizard may have been a 'plot device' to show pokemon that disobey, but it was important because it showed that not even Ash could 'wow' every pokemon with a couple days of friendship. It also was an indication of Ash maturing IMO. ^^