Blending at Model Level vs Blending at Story level in SAP Analytics Cloud(SAC)

Friends

I could see minor difference with regard to blending option in SAP Analytics Cloud

Join types used while Blending/Combining at SAC Model level are only 2

1)Primary data

2)Intersect data

Join types used while Blending/Combining at SAC Story level are 3

1)Primary data

2)Intersect data

3) All data

Is this a product limitation? please share your experiences

Reg-Bose