All files are encrypted on the hosts and only can be decrypted with the key, usually present only on the storage buyer's machine. All files are uploaded to 3 different hosts to avoid issues if someone flakes out, and could be to more if needed and every hoster puts some money on the line if they fail to host the files, providing a sort of financial insurance policy. This may not be good enough for every scenario, but I think for most it offers the possibility of covering things quite well.
There are only a few major cloud storage providers around, the market just isn't that big and they're all quite expensive comparatively - for long term storage of backups and low-value data I find it quite a good concept. Publicly accessed data like S3 is often used for, not so much, that's more of a target for a traditional cloud provider or something like IPFS in the distributed world.
Sia's more creating a new market for extremely cheap, reasonably reliabile storage rather than replacing one for expensive very high reliability storage in my view. But by nature of the way the network works, it should be possible to tell the # of hosts needed to match Amazon or Google in reliability - it's not in a state where all of that's possible yet though.
> facing significant legal repercussions.
There's nothing illegal about price discrimination, it's a common buisiness practice and something companies strive for - they want to make sure you pay the maximum price you're willing to. To do otherwise is essentially a failure to their investors.