Rust's (and other languages) memory safety doesn't come from hardware features. Implementing memory safety at the language level means that you don't care about

Rust's (and other languages) memory safety doesn't come from hardware features. Implementing memory safety at the language level means that you don't care about whether the data sits in a paged mapped as read-only, because the language already makes sure you're not writing to said data. Besides, that's the safety of the code running inside the VM. Wasm is about the safety of the host.