I think it would be good to consider :
a) Are these digital memories meant to be stored forever? (does the late night party swigging which went on fb/instgram/wherever have to be around by the time the kids arrive?)
b) possibilities of Cloud storage.
c) CG generated graphics and movies - especially the 3d ones?
I am not saying either medium is *better* for storage, I am saying it needs to be compared a little better.
To qualify: I lost a 400Gig HDD a year back - it fell 1.5ft onto the ground and then poof. I generally have the strategy of HDD+ HDD+ optical medium(when I can). That time, it was my main HDD and I didnt have *some* of the pictures backed up, well nearly half a year's worth of travels. Then again, my processing of one of my Kumbh Mela rolls went kaput also...