Yes, decision theory has been floated as a normative standard for human rationality. The trouble is that the standard is bogus. Conformity to the full set of axioms is not a rational requirement. The Allais Paradox and the Ellsberg Paradox are cases in point. Plenty of apparently very intelligent and rational people make decisions that violate the axioms, even when shown how their decisions violate the VNM axioms. I tentatively conclude that the problem lies in the axioms, rather than these decision makers. In particular, the Independence of "Irrelevant" Alternatives and some strong ordering assumptions both look problematic. Teddy Seidenfeld has a good paper <pdf> on the ordering assumptions.