I have a theory that the tests which have shown that it is difficult to
extract calcium from green leafies may be biased by the fact that most
people eat diets high in cereal grains and dairy; apparently glutens and
other substances can build up on intestinal walls.  It may well be that if
you clean your system out of these things (especially the grain) your
body's ability to absorb these minerals may be improved.

Also, in the absense of cereal grains, it is highly likely that your body's
NEED for calcium intake will be diminished; normally the amount of calcium
recommended is based on what a normal person (eating a normal diet) needs
for health.  Well of course if a normal person is eating lots of cereal
grains, they will need more than those of us who are grain-free do.