Well, George Mason is not a think-tank, it’s a university. Therefore, the palette of professors and administrators is going to be, by default, more diverse. Ludwig von Mises Institute usually attracts a very specific set of minds, although, ultimately, I don’t think the professional core of either are really that intellectually opposed. Of course, many economics professors at GMU are not Austrian, at all (Bryan Caplan, Tyler Cowen, Walter Williams, et cetera). It’s also important to distinguish between people who blog with GMU professors, but are not GMU professors (Horwitz, Rizzo, et cetera).
Regarding Hayek versus Rothbard, it really depends on the professor. Lawrence White is well read on Mises, given his attempts to homogenize Mises’s theories of money and banking with his own theories of free banking. Peter Boettke (who, as far as I know, is not a free banker [as in, a follower of Selgin’s and Whites’s theories]) uses Man, Economy, and State as one of his main textbooks. I don’t know the work of Don Boudreaux (the name of his blog, aside), Chris Coyne, Russ Roberts, Peter Leeson, et cetera, but I really don’t think it’s an issue of Hayek versus Mises. I think there’s a lot of focus on the fractional reserve banking argument, and it makes it seem as if they depart from Rothbard. In fact, though, apart from the issue of banking and, perhaps, other issues elsewhere, there are not many differences between the two. So, it doesn’t make sense to say that they ‘downplay Rothbard’. They might just source other people’s work, but agree with basically the same things.
I have infrequent crossings with Callahan, and it just seems that he dropped the moralistic approach to libertarianism. I think that this made him drop libertarianism altogether. I can’t really comment on his political beliefs, because I honestly don’t know them, and the same goes for his views on economics (maybe I don’t read his blog often enough). I’m not sure what he accepts or rejects anymore; I know that I’m critisized him on his views on overproduction, but Robert Murphy actually strangely agreed with Callahan.
Also, I think it’s worthwhile to comment on something said in another post above mine. Hayek did not ‘essentially reject praxeology’. If you’ve read his comments on methodology in Monetary Theory and the Trade Cycle and The Counter-Revolution of Science, you know that his methodological position is actually close to that of Mises. Hayek did not consider himself a praxeologist, and of course his methodology was not praxeology, but it’s disingenious to make the claim that he ‘rejected’ praxeology. Hayek’s and Mises’s methods of economic study were actually quite similar. Furthermore, if anybody has respect for Hayek it’s not because of his views on praxeology, but because he simply has had a large impact on the Austrian tradition since the early 1970s. By the way, many of the fractional reserve bankers have written extensive guides to praxeology, including George Selgin.
Also, praxeological economics has nothing to do with political views, so a rejection of praxeology is not what causes leading one to believe in the validity of the state. Hayek came to Misesian economics with a much more different social perspective, and so there is no reason to be surprised that his political views were different to those of Mises. Furthermore, these political views have no bearing on Hayek’s popularity within academia.