I'm going to disagree with what you said =/ Paul does in fact gain respect for Ash, really starting when he finds out that Ash was able to defeat Brandon the Battle Pyramid King, who then defeated Paul without losing a single Pokemon. Additionally, after Ash finally defeated Paul in the Sinnoh League, when they parted, they left on good terms and I'm pretty sure they had mutual respect for each other
After a fierce battle in the Sinnoh League Tournament, Paul was finally defeated and he and Ash parted on good terms, Ash having earned Paul's respect and ending their rivalry.
In regards to Paul's background, I'd say it stems from his Brother. Paul witnessed his brother lose to Brandon completely (shown in a flashback), and since Reggie (Paul's brother) has a battling style not dissimilar to Ash's (trust and stuff :P)
Unlike his younger brother, he treats his Pokémon with love and care and thanks them after working hard in a battle.
Paul probably felt that the way his Brother fought was weak (also because his brother quit battling after losing to Brandon). Because of this Paul's battling style is just to use the strongest Pokemon, and release all those too weak to meet his standards (Reggie said Paul had a cruel streak) - additionally he only has respect for strong Trainers like Cynthia and Brandon, and later Ash (Probably since they all beat him xD)