From Instapundit: Dave Winer defends the Dean Scream and gives a behind the scenes look at it. I don't know who this person is and therefore his credibility is somewhat suspect, but his explanation of why he screamed makes good sense. The Media of course can't grasp the answer, because it does not fit the mold of Dean they have already made.
Now, why Glenn Reynolds linked to this could be judged as a bit "Negative" Dean support. Glenn might want Dean to face Bush, so why not help him anyway he can. Reyonlds has political influence, especially in the primary stages, so saying he is being Machiavellian is not as big of a reach as it may seem.