How come people cheat and at the same time claim the moral high ground?

Newsweek's Sharon Begley explains:
"...In a new study that will not exactly restore your faith in human nature, psychologists David DeSteno and Piercarlo Valdesolo of Northeastern University instructed 94 people to assign themselves and a stranger one of two tasks: an easy one, looking for hidden images in a photo, or a hard one, solving math and logic problems...Then everyone was asked, how fairly did you act?, from "extremely unfairly" (1) to "extremely fairly" (7). Next they watched someone else make the assignments, and judged that person's ethics. Selflessness was a virtual no-show: 87 out of 94 people opted for the easy task and gave the next guy the onerous one. Hypocrisy, however, showed up with bells on: every single person who made the selfish choice judged his own behavior more leniently—on average, 4.5 vs. 3.1—than that of someone else who grabbed the easy task for himself...

"...DeSteno said, it may be because "we have this automatic, gut-level instinct to preserve our self-image. In our heart, maybe we're just not as sensitive to our own transgressions." Adds Dan Batson of the University of Kansas, a pioneer in hypocrisy studies, "people have learned that it pays to seem moral, since it lets you avoid censure and guilt. But even better is appearing moral without having to pay the cost of actually being moral"—such as assigning yourself the tough job....

""Since it's a cognitive process, we have volitional control over it," argues DeSteno. That matters because of another nasty aspect of hypocrisy: we apply the same moral relativism when judging the actions of people like ourselves. When "people like us" torture, it's justified; when people unlike us do, it's an atrocity..."