I’d agree with that, SPOOFE. It seems as if the kind of moderate you mean, per your OP, would be someone who–regardless of their ideology–attempts to weigh facts impartially, someone who is willing to accept compromise or acknowledge shades of gray, someone who is honest enough to reexamine their position in light of evidence to the contrary. Someone who sees the two prevailing sides to an issue, and is able to find merit and deficiency in both. Does that sound about right?
Of course, even given those parameters you have to identify and exclude politicians whose beliefs are so lightly held as to be subject to change as circumstances and self-interest dictate; such people are less moderates than Machiavells.
It might also be acknowledged, then, that there are certain issues for which there is seemingly no moderate position. Which, in turn, begets another type of moderation: What if a politician had no intrinsic opinion on abortion, for example, and was personally content simply to follow the rule of law on the subject? Would such person be considered a moderate, or simply weak of conviction?
Defining such things is muddy indeed, especially considering the entrenched “left-right” polarity perceived to exist in American politics. I view the moderate described in your OP as basically the antithesis of the ad hominem partisan we’ve discussed before. Position along the spectrum in a multiplicity of issues matters less, in that case, than a general intellectual honesty.
Which brings me to my answer for your question. We might be able to reach a considered consensus here about which politicians we thought to possess moderate qualities (or, more likely, which decidedly lacked those qualities), and inherent in our individual judgments would be a fair amount of bias towards people who held our positions or thought in the same manner that we ourselves think. I, personally, think that Paul Wellstone–an unabashed progressive liberal–to be moderate in his temperament; you might disagree. (And I hope that, confronted with evidence to the contrary, one of us would be able to change our mind.) But I’m sure that every politician–as every person–thinks themselves to be moderate in this manner. You’re not gonna find many who’ll cheerfully acknowledge, “Yup, I’m a myopic ideologue and proud of it!” Everyone claims to have the facts (and objectivity with which to judge those facts) on their side. In short, it’s tough to tell. 
(Oh, and a quibble–I’d say the centrist ideology is more concerned with maintaining the existing power structure than with keeping the majority happy. A small but important distinction.)