First, I think that requiring the reader to know the code in depth is a good thing. Comments should not be used to avoid this. Comments can decay in relevancy and, aside from function API documentation, should not be used in debugging. The way comments should be used is:

1) API documentation says this: does the code conform? If not, either the specification is bad or the code is bad.

2) Comments inform collaboration, but do not inform debugging other than as API documentation.