Ike, Bridgier's right. No equivalencies can be drawn here.
Silky was a Presidential candidate, not VP.
The rumors of his affair swirled well before, during, and after his candidacy, instead of just right after the race was entered.
The NY Times and WP had to admit they hadn't even bothered to investigate, let alone print the allegations against Edwards because they just couldn't find enough resources to commit. But then when Palin's daughter turned up pregnant, staffing must have gotten better. Somehow the Times managed 3 front page stories in one day.
All told, though, I have to agree with Bridgier. Equivalency would be a tough case to make.