Quinnipiac Polling's Peter Brown tries to explain why their polls don't weight Democrats and Republicans by their expected vote shares

It seems pretty obvious that you should weight the samples by what you think that the Democrat and Republican vote shares will be.  They weight the vote shares by demographics for race and age and gender.  The same should be true for political affiliation.  From the Hugh Hewitt Show's website:

. . . HH: I want to start with the models, which are creating quite a lot of controversy. In Florida, the model that Quinnipiac used gave Democrats a nine point edge in turnout. In Ohio, the sample had an eight point Democratic advantage. What’s the reasoning behind those models?
PB: Well, what is important to understand is that the way Quinnipiac and most other major polls do their sampling is we do not wait for party ID. We ask voters, or the people we interview, do they consider themselves a Democrat, a Republican, an independent or a member of a minor party. And that’s different than asking them what their party registration is. What you’re comparing it to is party registration. In other words, when someone starts as a voter, they have the opportunity of, in most states, of being a Republican, a Democrat, or a member of a minor party or unaffiliated. . . .
HH: Now what I don’t understand this, so educate me on it, if Democrats only had a three point advantage in Florida in the final turnout measurement in 2008, but in your poll they have a nine point turnout advantage, why is that not a source of skepticism for people?
PB: Well, I mean, clearly there will be some people who are skeptics. This is how we’ve always done our polls. Our record is very good in terms of accuracy. Again, remember, we’re asking people what they consider themselves at the time we call them.
HH: But I don’t know how that goes to the issue, Peter, so help me. I’m not being argumentative, I really want to know. Why would guys run a poll with nine percent more Democrats than Republicans when that percentage advantage, I mean, if you’re trying to tell people how the state is going to go, I don’t think this is particularly helpful, because you’ve oversampled Democrats, right?
PB: But we didn’t set out to oversample Democrats. We did our normal, random digit dial way of calling people. And there were, these are likely voters. They had to pass a screen. Because it’s a presidential year, it’s not a particularly heavy screen. . . .
HH: I mean, you really think that’s true? I mean, as a professional, you believe that Democrats have a nine point turnout advantage in Florida?
PB: Our record has been very good. You know, Hugh, I…
HH: That’s not responsive. It’s just a question. Do you personally, Peter, believe that Democrats enjoy a nine point turnout advantage right now?
PB: What I believe is what we found. . . .