It's more precluded possibilities versus actual events - Bruce lost his parents at an early age, so all he has to remember them by is his memories as a little boy, which inevitably means that he tends to put them on a pedestal. He never got to know them as the complex individuals that they actually were, just as the parents that he loved in the uncomplicated and direct fashion of a little boy - had the mugging occurred during his mid-teens or later, he would have developed a different relationship to them, and his reaction to their death might not have been so extreme. Clark, on the other hand, HAS had a chance to get to know his parents as more complex individuals, and to his considerable luck, they really are as salt-of-the-earth as Bruce only imagines, but can never know, his to be - Bruce's examples are idealized and dead, Clark's are truthful and alive (except in Pre-Crisis continuity, but even then, they lived long, full lives before they passed on).