The progressive pushback against the Senate health care bill has been, and will continue to be, essential in creating any space for the bill to be improved. Both during the final process putting together the substitute amendment in the Senate, and during the upcoming conference committee, whatever small improvements end up in the final legislation will / would not have been possible without people like Howard Dean, and groups like MoveOn.org. If no one was making noise from the left about how terrible the Senate bill is, and instead if everyone had been saying how the bill was teh awesome, then there would have been no reason to improve the bill at all. If anything, the bill would have been weakened even further.
Still, whatever small improvements are made will be crumbs compared to what Lieberman. Ben Nelson, and insurance companies have been able to wring from the process. Why were they able to win so much more from the process than progressive organizations, activists, and members of Congress? There are a lot of pet theories floating around, but the only explanation that can be easily backed up by quantitative analysis is that President Obama is the only person with enough sway over enough of the progressive base to have been able to translate progressive dissatisfaction with the bill into transformative action to improved the bill. However, he just didn't use that influence to change the bill in ways that meshed with the aims of the progressives who are now calling the bill unsatisfactory.
According to Gallup weekly tracking, over three-fourths of self-identified liberals still approve of President Obama's job performance. Over the past week, his approval among liberals actually went up 1%, despite the big left-wing revolt.
If there was going to be a national left-wing revolt to defeat the bill, it was either going to have to be led by President Obama himself or by an alliance of progressive organizations with equal sway over the progressive base. However, no such alliance exists. No one has the same sway over the progressive base as President Obama, or really anywhere even close. If there was ever going to be a left-wing revolt that resulted in more than crumbs, then President Obama was going to have to lead it himself. However, he never did that, or made any indication he ever would.
It isn't so much that President Obama takes self-identified liberals for granted--its more like he has he has convinced the vast majority of self-identified liberals to join him in supporting policies like Liebercare. If progressive organizations are going to win more than crumbs in future fights, then they need more sway over the progressive grassroots base than even President Obama, (or whoever happens to be leading the Democratic Party at any given time). That is a monumental organizing task, but it is what left-wing opponents of this bill currently face. You can't win a political fight when your opponent has more sway among your community than you do. And, right now, President Obama's sway among the center-left rank and file in America remains unchallenged.