The first case is why we have data retention laws.
On the second, I _think_ that in most jursidictions in the US the moment you're arrested you have an impetus not to destroy evidence that probably extends to not allowing evidence to be destroyed by a system that you could trivially prevent.
Putting a system in place where you have to take action to prevent an event is legally similar to a system where you take action to cause an event; in either case you've purposely taken an action that leads to the destruction of evidence.
We'd need a real lawyer to comment, but otherwise I think we'd have already seen things like this for years (even pre-computer)