The most important point per JK Rowling

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No: HPFGUIDX 134584

JKR:  The "crucial and central question" of the series is why both 
Harry and Voldemort survived the killing curse. [Read the exact quote 
from World Book Day, 2004]

Rowling has said we should be asking why Voldemort lived -- not 
Harry.  Could it be that Snapes was there and somehow prevented 
Voldemort's death?

Or does this have to do wit the horcruxes?