I have reviewed the descriptions of the built-in functions in Python 3.4, and found only the following issues w.r.t. missing __special__functions:
1. getattr(), setattr(), delattr(): They only refer to object attributes and miss to mention the fallback to object.__getattr__(), etc. Because hasattr() calls getattr() to test for the presence, the __getattr__() is relevant for hasattr() as well.
2. len() misses to describe that it uses s.__len__().
3. sorted() misses to describe how rich comparison methods can be used. I think we can integrate the changes to list.sort() proposed in issue14050.
4. str() delegates the description to stdtypes.html#str, which in turn does describe obj.__str__(). Not sure we need to do something for str().
I did not check 2.7 yet.
Andy