actually it does, in purely holistic design terms
to the laymen, there is no real difference since both will be perceived as "brothers" with X6 being newer, just because they are the 2 large SUV's that BMW is offering for sale
but in more design terms, knwing the origin of a design gives better insight in understanding the how, and the why that came to be X6 or whatever else at the end
having the premium SUV design starting at the X6 side, before being adapted to X5 enables to understand the origin of this particular design in sporty and dynamic come utilitarian, specially in the X6, where it was toned down to make it more utilatarian for the X5

it\s not really a big deal, but when analyzing a design it\s important to know, were the lines softened or hardened? the creases lessened or made deper during the process?
were thees in light of a different philophic approach? (nature of X5 versus X6) or to market research and curtomer reaction (X5 sales versus X6 preview and studies)?