Archive.org can archive Twitter and IMDB but both Twitter and IMDB do not have libre/free licensing for user generated content.
Here is HNs policy [0]:
"""
Commercial Use: Unless otherwise expressly authorized herein or in the Site, you agree not to display, distribute, license, perform, publish, reproduce, duplicate, copy, create derivative works from, modify, sell, resell, exploit, transfer or upload for any commercial purposes, any portion of the Site, use of the Site, or access to the Site. ...
"""
If HN ever folds, the most likely condition will be someone owns the copyright and will not put it under a libre/free license for the community to use, effectively burying it. In the meantime, HN offers a (perhaps small) treasure trove of information about technical issues, trends, data on how a community forms, communicates and interacts with each other that is explicitly barred from use by the general public without individual approval.
Though this would probably be met with a lot of resistance, HN is well within their right to sue all the "show HN" projects that use the HN data to display interesting trends, do data analysis or do other interesting projects with.
