I don't see why our preferences can't be expressed by a utility function even as they are. The only reason it wouldn't work out is if there were circular preferences, and I don't think most peoples preferences would work out to be truly circular if they were to think about the specific occurrence and decide what they really preferred.

Or they might violate the independence axiom, but in any case what do you mean by " think about the specific occurrence and decide what they really preferred", since the result of such thinking is likely to depend on the exact order they thought about things in.