In web terms: - Element is like a browser - matrix.org is like a bulletin board

In e-mail terms: - Element is like a mail client - matrix.org is like a given community of mailing lists

In IRC terms: - Element is like an IRC client - matrix.org is like an IRC server/network e.g. Freenode.

Matrix.org is just one server deployment that implements the matrix protocol. You can deploy your own server or even your own implementation, and moderate it how you want. It has nothing to do with element. The apology is apt, as just like a browser speaks http, element speaks matrix.

Element is just one of many Matrix user agents and matrix.org offers just one of many Matrix servers.

Each server has the freedom to enforce its own policy. Given that the matrix.org server is a kind of a public face for the protocol, it makes sense that its policies are more mainstream.

There is nothing in the protocol itself (nor in the official Element clients) enforcing any kind of content policy.