Body knowledge and freedom of movement with well-developed coordination is indeed the foundation for all learning. It is how we explore our environment initially and how we represent it cognitively later.
I have spent the last year lecturing all over the country about the importance of early motor development and its role in learning and performance. Working with our patients in vision therapy, I found that many had poor integration of early motor movement patterns and often these primitive reflex motor patterns would dominate visual motor performance because the patient did not have the body knowledge to integrate these movement patterns into more intricate voluntary movements. Their movements were not well coordinated or visually directed nor was the patient even aware of how they were moving their body.
This problem does not go away with age -- they do not outgrow the problem. They simply learn to compensate or avoid activities which require more integrated movement then they are capable of achieving. These problems interfere with their ability to achieve their full potential.
I can't help but wonder if the proliferation of baby "contraptions" (carriers in which the baby can sit during transport, in the car, on the counter, etc.; swings in which they sit to be entertained; walkers or jumpers which artificially support their little bodies while preventing them from exploring their own control, etc.) are leading us to a generation of "bucket babies" with poor motor integration. I am certainly seeing more problems in my practice than I did 20 years ago. What Rachael is offering is a way to avoid this problem by creating opportunity for natural learning.
The movement activities Rachael recommends play a key role in the integration of the primitive reflex movements during the developmental stage where it is most appropriate.