I agree with your point that changing a position should not be categorically dismissed as weakness, as it typically is in recent US politics. Obviously there are limits to this and IMO, a lot of what you see is a reaction to the impression Clinton did not have any principles. I think in the next 5 years or so you will see something quite the opposite as people will have an impression that inflexibility has been one of Bush's bigger weaknesses.
I think your math analogy is a poor way to get the point across. Equating conservatives to someone who answers 5 to every question is silly and belittling. Besides conservatives can always reply that their principles are more analogous to the following ones.
<ul type="square"> [*]A straight line segment can be extended indefinitely in a straight line[*]All right angles are congruent.[*]If two lines are drawn which intersect a third in such a way that the sum of the inner angles on one side is less than two right angles, then the two lines inevitably must intersect each other on that side if extended far enough[*]If equals are added to equals, then the sums are equal.[*]Things which equal the same thing are equal to one another.[/list]
It is notable that there has been a big shift as Liberals used to be seen as the idealists and Conservatives seen as more pragmatic. That has flipped pretty dramatically in the last 4 years or so.