a: 1
    b: 2

    obj: {
      a: 1
      b: 2
    }

Quite right, and internally, both kinds of assignment compile into a CoffeeScript AssignNode. The latter is just tagged as occurring within an object literal. Having the commas be optional in multiline objects also helps make both kinds of assignment look identical.

(And I'm calling it assignment because saying "binding" in JavaScript usually means that you're binding a function to a "this" context object)