Politics is about: power, how a society organizes itself, how communities interact with each other, and generally who gets what and why.
Economics is about: incentives, transactions, cause and effect, and the machinery/workings of an economy.
There is undoubtedly overlap between the two, but I wouldn't say that either is a subset of the other, and I think it would stretch the bounds of what a site about politics means to say that questions on economics, even narrowed to just macroeconomics, are wholly and always within scope.
Economics provides an extremely powerful toolkit for analyzing how things work, but it is not all powerful. Economists I think fall into a trap of assuming that since they can come up with a model for a situation, they understand the situation. xkcd has a great comic about this problem with respect to physicists.
I'm not trying to bash economics here. I think Affable Geek is right that macroeconomic policy is almost completely intertwined with politics. I think economics is great for providing a framework for getting close to an objective analysis of a situation, but not always well equipped for providing a normative analysis of that same situation. Normative judgments seem to be much more within the purview of politics.
To more directly answer Chad's question, I think as long as a question has a political hook to it it should be considered in scope. If it is just about the soundness of an economic policy solely from an economics perspective that seems to be less about politics. On History we try to make sure that questions have some attachment to the history of the situation or historical impact etc. I think the same considerations are valid for politics.