> the core OS enjoys tremendous success and market share.

How is that relevant? OSX has at best around 10% global market share? I'm talking market dominance here.

> How do you determine the invariants of your APIs when writing code against a module?

We flick through the well-documented code just as you would largely ignore the code and flick through well-documented comments. Here is a simple example for you:

public class EntitySynchroniser : IEntitySynchroniser
{
public EntitySynchroniser(BusinessObjectFactory factory, IDirectorySearcher directorySearcher)
{
Argument.NotNull(factory, "factory");
Argument.NotNull(directorySearcher, "directorySearcher");
this.factory = factory;
this.directorySearcher = directorySearcher;
}
...

The arguments here are invariant - they must not be null. I don't need a comment that may or may not be written in precisely the same format between 100 developers maintaining the codebase. I simply look for the one call to Argument.NotNull that all developers use in this case. The code is MUCH more readable than if the constructor had a comment explaining that each should not be null, mixed in with explaining what each should do. I can also determine by file searching or through the IDE which methods have these requirements.

If readers want to know what this API is and what it can do they need only look to the interface, or the implementation of it's methods in the class. Each method explains what it does by maintaining the same level of abstraction within the method. Like:

public void MethodA()
{
DoFirstHighLevelThing();
DoSecondHighLevelThing();
}

void DoFirstHighLevelThing()
{
// do less high-level things
}

Each method call would maintain a constant level of abstraction so that the code is easily reused, easily tested and easily maintained.

> You're just wasting your time somewhere else, in little tiny increments, every time you have to trace code a few steps down just to figure out what it probably is supposed to do.

If I needed to figure out why code wasn't working the way it should what's to say a comment would be more forthcoming in explaining the reasons for the defect? Surely if MethodA did "thing A" but was really doing "thing B" the comment would tell me "thing A", therefore I'd be forced to examine the code further anyway, only I'd be hampered by the deceitful comment also? This is the nature of a defect - something that operates outside the documented behaviour of the system or module.

Not to mention that your stated opinion is that comments should explain the inner workings of things so that consumers can be well informed. This has the potential for exponential maintenance as really low level changes are made. Imagine that you change the conditions under which data access-level exceptions are raised. If anything that ever touched your data source explained what happened in exceptional circumstances you'd have to change hundreds or thousands of comments, or face the sort of comment rot I mentioned earlier. This is the real time waster!

> ...when somebody new has to learn the code base.

This is always going to be the case. Comments don't make this task any easier than a well structured codebase. A well structured codebase comes from developers making the conscious decision that any reliance on the crutch of a comment is a failure to write proper self-documenting code. A well-structured self-documenting codebase by definition requires no comments (except for the "why" not the "how", which I fully support doing by the way).