Have you considered the inequities that such a retention policy introduces into HOW history can be used?
The entrepreneurial (and governments) will archive everything to serve the wealthy (including governments), who will be able to use history to their ends. Those without resources will live in an eternal present, except where history is used against them.
To sell this kind of retention policy as a user-protecting feature is (in my view) at best naive, and at worst, disingenuous. This model increases the economic cost of mining history, but in doing so, entrenches existing wealth and power structures.
Thanks to the ever-decreasing cost-per-bit of storage, the internet is forever. The only hope for redemption lies in this permanence affecting everyone equally; otherwise we're doomed to (continue to) live in a world where only the wealthy and politically connected have read and write access to history.