Does our culture shape our expectations about knowledge and certainty?  The U.S. as a positivist culture...

The United States, in my experience, is the last holdout of an epistemological stance called positivism. Positivism is a belief about science and scientific knowledge that emerged towards the end of the Enlightenment. Basically, it holds that

i) the only acceptable knowledge is certain knowledge - any knowledge claims which are less than certain are to be rejected along with the demonstrably false claims (following Descartes' project of doubt), and

ii) the only domain for achieving certain knowledge is the domain of natural science. Natural science, with its mixture of mathematics, empirical investigation into cause-effect relationships, and resulting theories (apparently) capable of prediction and control over nature, becomes the paradigm against which all other forms of knowledge must be measured.

Not surprisingly, very few forms of knowledge - including traditional claims and issues in philosophy and religion - can measure up to the demand for absolute certainty, and so they are rejected.

If American cultures teaches such positivism - then it badly prepares us for (a) understanding how the natural and social sciences really work, and (b) accurately assessing diverse forms of knowledge (ethical, philosophical, religious, aesthetic, narrative, etc., alongside scientific claims).

Simply, the positivist paradigm and its demand for certain knowledge is mistaken. Positivism can be shown to be mistaken on philosophical grounds (e.g., epistemological arguments of a Kantian sort), scientific grounds (especially the advent of quantum mechanics and the shift to probabilistic analyses, relativity theory, etc.) and mathematical grounds (Goedel's proof, perhaps chaos and complexity theories).

"Post-positivist" epistemologies shift from the simple "either/or" - either absolute certainty or absolute falsehood - back to "epistemological continuums," i.e., the recognition that even the best scientific work will often issue in either limited claims (e.g., the greater our determination of the position of a particle, the less we can know regarding its velocity) and/or claims of varying degrees of probability and certainty. Most brutally, the fundamental assumptions regarding nature and humanity's ability to know nature which shape the methodologies of the natural sciences cannot themselves be proven using strictly scientific techniques. (This is part of the problem raised so forcefully by Goedel's proof, which demonstrates that no axiomatic system can be both complete and consistent.)