While it's true that many online solutions could be risky, I would trust the lifespan of Amazon over a consumer-grade hard drive.
You are aware that some lost everything in the recent Amazon crash?? Some lost their files when their online photo services folded. Online storage has not really been proven to be a reliable system that you can upload to and expect to have your data 50 years from now. Nor is a hard drive, raid system, SSD, memory card, DVD, or CD.
You must actively keep multiple backups and move data as media becomes obsolete. That was my point, nothing is as reliable as those 100 year old prints that many of my cousins have in a shoebox in their closet. Some may be lost, some may burn up, but there seem to always be someone who managed to save them. I guess thats a case of many many backup copies to a media that does not lost the images after 50 or 100 years.http://www.businessinsider.com/amazon-lost-data-2011-4
My Grandfather from around 1905. You had to sit very still then, no fast lenses or shutters.
My Grandmother born in 1886
The point is that we still do not really have media that can match the longevity of the old prints from 100 years or more ago, except to make and store prints.