Chalk it up to the claimed and accepted "greater experience" of the Clintons that Hillary's campaign got dirtier sooner.
Chalk it up to Obama's higher regard for the American voter that he was explicitly reticent and wary in practice about being negative and feels the need to announce that his campaign will now add such tactics to its arsenal.
I personally am cast into a weary disappointment by these developments.
Once someone is elected, the other guy and all that was supposedly wrong with him or her is ancient political footnotes and leaflets in a dumpster. What will be...or more to the point of this process, what we hope will be...is the substance of the candidate's policy ideas, the quality of the advisers they attract, their power to persuade and inspire the broadest spectrum within the electorate. In a word, the positives: who they are, what changes they will propose, how good they are at educating voters on the issues how well their choice of issues reflects the needs that people feel. The positives should dominate the campaigning.
I think this sour turn in the Democratic campaign betokens Clinton knowing and Obama finding out that the American voter is a cheap beast, easily bought by appeals to their insecurity and despite what they tell to pollsters, fond of a little blood on the campaign trail. It is sad to see what works and what does not work on the American voter...and maybe they are not so different from a German voter or an Italian voter after all.
The nearest thing to a silver lining is probably that the swift boaters McCain can count on without even the embarrassment of a phone call and his own attacks will finally be thrown at whichever Democratic candidate has the least to hide and has been the best at catching spears in mid air.