Very interesting! From what you've said here, Steemit would not fall under this regulation as Steemit does not store private keys. Steem is based on Graphene, the tech behind Bitshares, and therefore uses a similar model to Bitshares where the private keys are only kept in the browser and used to sign the transaction locally, and this transaction is then broadcast using an API server.

This post by @dantheman explains how keys are generated from your password. You can also log in using your private key directly.