Because of those two camps, Republicans are displeased with their congressional representitives because there are people of both camps in congress, meaning there are people in congress members of both camps can be disapproving of.
In all reality the polls show that things are rather normal in terms of your independents. More than 2/3rds of Democrats support the congressional Dem's, and the support for them hovers just under the national percentage of Democrats. The Republicans have a significant split, with over half the party being disapproving, so its explains why their approval number is lower. The President, historically, polls better than congress because its easier to express displeasure for the faceless entity that is the house and senate.
Its a heavily slanted reading, that bears little factual evidence when one looks closely at the results of the poll, to suggest that the low approval of what Republicans are doing and higher approval for what Obama is doing equates to significantly more people WANTING what Obama is supporting.
Additionally, you'd note, that none of the three entities that had the poll done about them recieved over 50% approval and all three had more disapproval than approval.