A lot of the changes for 0.6 are removing keywords from the grammar. In this case, the `static` keyword has been removed, so there must be another way to tell if a method is static.

Another reason might be so that self can be passed in a way the programmer prefers. Usually this appears to be `&self`, but it can also be passed in other ways.

Disclaimer: I work for Mozilla on Servo, and am still getting fully up to speed on Rust.