A theory is an educated guess, which is not a belief, but indeed, many theorists believe in their theories to be fact.
The distinction I am making is that philosophic belief systems, which I appreciate and understand your fairly accurate point, deal with possibilities, probabilities, and the ability to change.
Whereas the belief systems to which I was referring... do not.
A philosphy is a belief structure based on what we know.
I would say it is a structure of greatest probability, not belief. To believe is to think you know without doubt, and with no chance of variation.
Philosophies, being working theories, are open ended and do not permit unchangeable belief.