This is an interesting question that I have been busy looking into from another perspective.
In the last weeks two papers have been published about sensory processing and toewalking and the processing of sensory information in children with autism spectrum disorders (ASD).
1. Abstract | Idiopathic toe walking and sensory processing dysfunction article on Idiopathic toe walking and sensory processing dysfunction in the online Journal of Foot and Ankle Research 2010, 3:16doi:10.1186/1757-1146-3-16
2. Autism linked to multisensory integration
A new study by researchers at Albert Einstein College of Medicine of Yeshiva University has provided concrete evidence that children with autism spectrum disorders (ASD) process sensory information such as sound, touch and vision differently than typically developing children.
The thought has crossed my mind that the reason why children (not only those with autisme) toewalk could possibly be because of a need to "stimulate" their own sensory systems.
I would like to hear what others think about this idea.