Because it relates to a supposedly HIGHLY classified program.  In all honesty, if I were the Republicans, I'd be totally panicked about this story.  If it in fact is true, it means that Bush HAS NO CHOICE BUT to fire Rumsfeld, based on his own statements about tracking this up the chain of command and punishing those responsible.  Failure to do so, if the story is proven true, then sticks DIRECTLY onto BUSH himself.  I think that it's instructive that John McCain and John Warner did NOT respond to this on the Sunday news shows as though it were the ridiculous bit of fantasy that YOU'D like to claim it is.  THEY realize the potential ramifications of this.

The fact is, IF this sticks, (and I admit that it is too early to tell if it will) it's a smoking gun right up Bush's rear end relating to his hypocrisy in dealing with the Arab world, and it's probably unrecoverable for Bush, in terms of salvaging the Iraq operation.  It remains to be seen as to whether it does, but it is by NO MEANS as easily dismissed as you'd like to claim it is.

And, BTW, Hersh has way too much credibility in the intelligence community to simply dismiss the story out of hand.  If he doesn't actually have a tracable story here, he's probably blown his career out of the water.  And if he DOES have such a story, at the very least, he has blown Rumsfeld's career out of the water, and depending on how Bush handles it, Bush is next in line to touch the 3rd rail.

Using apparently different sources than those Hersh used for his article, have essentially confirmed the essence of the story that Hersh wrote.  I read the account by the Boston Globe, which appeared to have been a subdued, controlled accounting of the chain of events and decisions that ultimately led to the conditions that ended in abuse of war prisoners.
   It appeared that the policy originally had some reasonable basis to it in that it allowed people like terrorists to be handled a little more roughly than soldiers from a country's military would be handled.  Interestingly, the policy was apparently opposed strongly by the great majority of military lawyers and apparently even the Judge Advocate and later by Colin Powell.  The concern that Powell apparently expressed was that by removing the cover of the Geneva conventions from even terrorists would ultimately subject US soldiers and citizens to torture and/or murder.  Citizens and soldiers have been killed by terrorist while in captivity as recently seen with Mr. Berg (an earlier situation took place in Lebanon where a uniformed US military deplomatic officer was captured and ultimately murdered, so it seems that if Powell's concern ultimately become reality, the difference will be in the numbers of US citizens who are tortured or murdered while in being held by hostile forces.
    It is difficult to tell how this prisoner abuse issue will play out, but one immediate consequence is that it is leaving us more isolated from allies than we have probaly ever been in my lifetime.  We can easily live without some of those allies but we cannot operate effectively witout the cooperation of others.  Even Great Britain, which has been stout in it's support maybe headed on a different path, there is information circulating that Tony Blair will step down as head of the Labor party and by default as the British PM.  Blair's fate was probaly sealed before the abuse scandal broke, but the abuse situation does not help him at all.  Blair follows Spain's former PM, who like Blair was strong in his support of us.

... the story is just too juicy to pass up.

Hersh usually gets it right.