The primary difference is definitional: The centerpiece of Edwards's campaign is his anti-poverty efforts; he presents himself as a dedicated messenger for the cause, and he likes expensive haircuts, bought a gimungous house, etc. etc. His credibility as a messenger comes into question when he spends money ostentatiously. (The haircut was inadvertently billed to the campaign, a spokesman later said).
There is a difference in the political reality: fairly or unfairly, a healthy chunk of the national political press corps doesn't like John Edwards.
Fairly or unfairly, there's also a difference in narrative timing: when the first quarter ended, the press was trying to bury Edwards. It's not so much interested in burying Romney right now -- many reporters think he's the Republican frontrunner.