"If it bleeds, it leads," as they say. Sounds reasonable enough that that sort of shit gets way overreported/sensationalized, while good deeds or events get ignored. It seems when you do hear about something nice happening, it's some kind of fluff human interest piece about a kid saving his hamster from drowning or some shit.
On a media-bias related note, the coverage of the recent Bush visit to Portland and the attendant protest was interesting to see. The Portland Tribune's article cited that lots of police planning kept things "under control", and quoted an attendee of Bush's $2000/plate fundraiser luncheon as saying that it was sad that they needed so much protection to exercise their civil liberties. At no point was there any question raised as to why there needs to be a heavily armed riot squad to face off against a bunch of unarmed pacifists (who, strangely enough, were not rioting). Or why the police were acting as security guards for a private function (to the tune of over a million dollars, thus far in the lap of taxpayers). Or why it was necessary to have one cop for every 5-6 people protesting. The entire tone of the article implied that the protesters were some kind of unsavory force that was a hair's breadth away from spinning completely out of control, and were only civil because of the stormtrooper riot cops. They're basically inventing a riot that never would've happened.