Clark Lindsey follows up on the previous discussion (with the typical ahistorical nonsense in the comments section about Nixon “scrapping” Apollo):

I think that if, say, Pete Worden had been chosen as NASA chief in 2005, his study would have set boundary conditions much closer that for the HLR than to Griffin’s and come up with a HLR type of architecture. Conditions on Constellation required that it avoid in-space operations at all costs, avoid multiple launches at all costs, and avoid development of any new technologies at all costs. Not surprisingly, all of that ends up costing a whole lot.

As someone once said, when failure is not an option, success gets pretty damned expensive.