as a doctor most of his life and the position he had before he took over as Governor of Vermont was a part-time position [or maybe he was a legislator part-time before he became Lt Gov].  Dean's entry into full-time, higher level politics was almost an accident [the prior governor died suddenly, then Dean became governor].

So, he may very well have known less about political organizing than BO.  

However, it was Dean who 1st started firing up the dems/grassroots about opposing GWB's policies, Dean who 1st began criticizing congress-critters for rolling over for GWB, Dean using the internet for grass roots organizing [he likes to say that the grass roots found him], telling people "you have the power," getting younger voters excited, etc.

Like Reagan before him, BO is riding into the WH on a wave of dissatisfaction, a wave started years ago by more liberal activists.

It takes time for ideas to trickle into the mainstream and to influence behavior.  The dems as a party, as well as BO as a candidate, have greatly benefitted from HD's initiative and efforts.