Fabian Pascal and RDBMS deficiencies in fully implementing the relational model

I'm reading, and enjoying immensely, Fabial Pascal's book "Practical
Issues in Database Management."

Though I've just gotten started with the book, he seems to be saying
that modern RDBMSs aren't as faithful to relational theory as they
ought to be, and that this has many *practical* consequences, e.g. lack
of functionality.

Given that PostgreSQL is open source, it seems a more likely candidate
for addressing Pascal's concerns. At least the potential is there.

Some questions:

1) Is PostgreSQL more faithful to relational theory? If so, do you find
yourself using the additional functionality afforded by this? e.g. does
it really matter to what you do in your daily work.

2) If PostgreSQL is *not* significantly more faithful to relational
theory than commercial RDBMSs, is it at least on the road to becoming
more faithful?

3) If PostgreSQL is not on the road to becoming more faithful to
relational theory and purity, why not? Is it due to the fact that
various SQL standards are themselves not fully faithful to relational
theory, and most RDBMSs have as a primary design goal to be faithful to
standards (which Pascal implies *are* relationally deficient)?

4) Which database, commercial or non-commercial, is most faithful to
relational theory itself, or is headed in that direction the quickest?

Dana