Two words: "self reporting". Just as libs think themselves "tolerant" when in fact many are hateful and intolerant of anyone that doesn't agree with their worldview (perfect example is the OP), this is just a reflection of how the various groups view themselves.
The libs view themselves as more willing to compromise. What isn't reflected in that survey is that to them, completely agreeing with them is to only way to "compromise". The libs view themselves as more willing to have people around them with different views, but that's obviously not the case.
This study is actually a reflection of how respondents view themselves rather than how they are.
What's interesting is that you guys don't seem to see just how totally you are projecting onto those you view as your political opponents. From making the stimulus have a huge tax cut component, to adopting what was essentially a Republican plan for health care, to adopting what was essentially a Republican plan to combat climate change, to offering enormous spending cuts in exchange for revenue increases, etc, etc, there have been tons of efforts by the Democrats to compromise.
I think the other elements of this poll that show why the conservatives in here are so woefully misinformed: they generally associate with people and news outlets that already agree with them. That's how they are able to convince themselves that the 'other guys' are just as inflexible. That's how when they see conflicting information like this they say to themselves "well I already know they are just as uncompromising as me, therefore when they say they want more compromise they are lying".
You don't need to be a rocket scientist to see how the parties differ on this, just go look at their campaign ads. When liberals campaign for things they talk about what they can accomplish for people or what programs they want to implement. Conservatives are far more likely to talk about how they will stick to their guns, how they are true conservatives, etc. Not wavering is simply seen as a far more desirable trait on the right.