It's less "eco-friendliness" than "sustainability" or "resilience"*: can these things continue? Batteries wear out, lithium for new ones is hard to come by, formats change (you're on safer ground with DRM-free stuff from Gutenberg, but still). Apocalypse is but one possibility. A gradual descent into a future with less readily-available energy is another. No running for the hills required, but energy-free or -lite entertainment and learning might be useful. * I realise these are buzzwords at the moment. Doesn't mean they aren't important.