It's important to remember that 'required' for a classical BibTeX style means broadly 'The output might look odd without this field': BibTeX is not really trying to do data validation!
When Philipp Lehman wrote
biblatex he looked carefully at what was and wasn't common in bibliographies and tried to make a sensible set of standard styles. He also set up
biblatex so that in the main missing fields (even 'required' ones) don't give badly formatted output, although from the point of view of looking up references it may be sub-optimal. The 'required' fields are therefore best viewed as a suggestion for the minimum set that are needed to have any kind of 'reasonable' output, and are deliberately kept to as small a set as possible.
If you wish to do data validation, you really need to look at a range of issues not limited to the simple question of 'which fields have some content'.