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Unbalanced Snow Loads

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ASCE 7-05 has provisions for "simply supported prismatic members" and "all other gable roofs."  Obviously, trusses are not prismatic and the later provisions apply to designs of trusses.  But, what load is intended to be used for the design of the structure itself? 
If the structure uses a truss I've been using the "all other gable roofs" provisions to match the truss reactions.  However, I was recently told that the "simply supported" provisions are meant for the design of the building, regardless of whether the framing is a rafter or a simply supported truss (for W<=20).  If this is done, the resulting design loads can be considerably different from the truss reactions.
I realize that snow doesn't know the difference between a rafter and a truss, but what is the intent of ASCE 7 with this regard?  Should the building be designed for different snow loads than the roof framing?



Eric Tompos, PE, SE