Seeing as how the out of the door price for 12PB of data hosted on RRD S3 storage @ 99.999999999% durability is roughly $300k/month, I'd hardly call it trivial.
I'm not sure how you've figured they have 12PB of disk (Or possibly more like 36PB due to replication for 11 9s of durability) just lying around. The whole meme that ec2 came about due to it just being extra capacity is incorrect. Same goes for all of the other services. Running a business whose MO is to keep lowering costs and make a profit on razor thin margins doesn't lend itself to lots of unused infrastructure. They aren't going to sink costs into infrastructure without realizing a return as soon as possible.
Server amortization costs, future cost calculation planning, depreciation costs, power consumption, etc are all closely calculated and factored into budgets. Just thinking they can support that much data for free and at no cost, or minimal cost because it feels good is naive.
Google, and Amazon could very well run within the archive.org network once it is up... and could very well offload a significant amount of data. The nominal cost is anything but near zero... just on the wear of hard drives alone, it will be costly.
My point was you can't rely on them to keep said data available. Not that they couldn't participate.. but I wouldn't trust anything less than a "Lifetime" (of the company) or a 25 year minimum commitment as anything but transient.
