That is a very euro-centric, post-modernist way of thinking.
What are caste system if not social?
What are far-flung familial relations if not social?
A definition of being "social" which only applies to societies where friendship is paramount, and friends come and go with ease is too limiting and leads you to solutions that can be awkward in other societies.
For example, in my country, we care deeply about family and ancestory--so much so that in every generation one member of the family is nominated to be the "memory keeper" (sorry, there's no translatable word) who keeps track of the geneology of everyone, and is expected at a glance to determine if a stranger is at least vaguely related to us.
Would a free form social graph be useful to us---not really. Our facebook pages are practically 90% family members, 10% people who through marriage will become family members.