First: Hillary Clinton is viewed as more liberal than Barack Obama? Both Republicans and Democrats agree about this, and, needless to say, both Republicans and Democrats are very, very wrong on this score. Apparently the power of perception is hard to break down.
Third: Over at Ezra's place, Neil points out that John Edwards, who is arguably the most progressive candidate, is viewed as the most centrist. This is potentially good news for both progressives and for John Edwards, since it means the candidate most likely to pursue a progressive agenda once he's in office is also the candidate who's most electable.
An possible explanation of this pattern is that Clinton and Edwards are racing to the median Democratic primary voter. Clinton knows she is perceived as too far left to win the general, so she is running as a conservative. Edwards knows he is perceived to be a White man from the South, so he is running as a raging red. Each is trying to people to perceive them to be the median hopeful who will balance progressiveness and electability (AKA Barack Obama). I'd say both need extreme hair cuts.
Clearly such a pattern in a huge sample of 3 observations can easily be due to chance. I am assuming hopefuls have had private polls which give similar patterns for months now.
The point is that maybe campaign proposals are opposite of perceptions not because the public is dumber than a flipped coin, but because the candidates are all campaigning against type for strategic reasons.