There is a CNN poll that I think backs the vote -

As you may know, the U.S. House of Representatives and the U.S. Senate are trying to pass final legislation that would make major changes in the country's health care system. Based on what you have read or heard about that legislation, do you generally favor it or generally oppose it?
39% Favor, 59% Oppose (chart)

(IF OPPOSE) Do you oppose that legislation because you think its approach toward health care is too liberal, or because you think it is not liberal enough?
39 % Favor (from previous question)
43% Oppose, too liberal
13% Oppose, not liberal enough

So it is only 43% who oppose the bill as being too liberal. The other 13% want it to be more liberal.
52% therefore support either this bill or a more liberal version - I'd say it comes under the role of an elected politician to be pragmatic about it, recognise that those 13% aren't going to get a more liberal bill anytime soon and that this bill is the best option, not least as a step towards that more liberal view.