At this point, _setAttrs and setAttrs are the same, however, _set and set are not. _set allows you to bypass readOnly and writeOnce attributes.
Wouldn't it make sense to have _setAttrs be able to do the same?

Right now I have code like this:

reset: function() {

    this.set(VALUE, this.get(INITIAL_VALUE)).

        _set(IS_BAD, false).

        _set(OLD_VALUE, undefined).

        _set(REMOTE_VALUE,  undefined);

},

This code is in the same class as the attributes. I can't simply have getters in those readOnly attributes because I need them effectively changed so their change events fire.

I admit, though, that using _set allows me to use constants, which _setAttrs wouldn't allow me to, and that spares me from typos and compresses better and, since _setAttrs simply loops through the
object calling set (instead of _set) it wouldn't save any execution time. So, it is just for the sake of symmetry and because there doesn't seem to be any point in having both setAttrs and _setAttrs.