In the first case, there is nothing preventing the development of software to overwrite data before unlink(2) is called.

In the second case, you can choose to trust or distrust the cloud storage provider. Trust being backed by contractual obligations and the right to sue if those obligations are not met. Of course, most EULAs for consumer products are toothless is this respect. On the other hand, that doesn't prevent companies from offering contracts which have some teeth (which they may do for business clients).