It seems as if Petruchio surprises even himself when he realizes that although he outwardly wishes to marry for money, when it comes to it, he is motivated by something else: the desire to love and be loved. Petruchio, rather than being domineering and selfish, is an observant man who quickly senses in Katherine something more than her outward shrewishness. He sees beyond the superficial (unlike Lucentio who falls in love with Bianca based on what he has observed) and aptly recognizes that her behavior is a masquerade, a tough exterior intended to cover her inner desire to be loved and valued. On top of that, Petruchio becomes so attracted to her spirit and her non-conventional nature that when he accomplishes his initial desire to "wive it wealthily," he takes his involvement a step further, making a great effort to help Kate develop, sensing that the true Kate, when she can be brought out, will compliment him well.
Part of what makes Petruchio so likeable is his apparent disregard for social decorum, particularly when he works to get Kate to abandon her shrewish exterior. For instance, he doesn't buy into the notion of "birthright," as we see by his refusal to treat Katherine as a woman of her status traditionally expects to be treated. Rather, Petruchio's treatment of Kate is based on how she behaves. She has to earn her privileges. We see another good example of Petruchio's willingness to go against convention in an ends-justifying-the-means fashion when he arrives late for the wedding. To be sure, though, it is this exact willingness to go against convention that keeps Petruchio from being a paragon for the Elizabethan man (remember, class and social stratifications were encouraged by those in power during Shakespeare's time). Many of the ordinary people who initially viewed the plays (they made up the bulk of the audience) would likely have seen Petruchio as a hero, but to those in power, aspects of Petruchio's behavior would have been cause for concern.
