I agree, but closures and bine are expensive--present in both cases. It's better to avoid it. Granted, this is a contrived example and sometimes closures are the more elegant solution.
function Person() {
this.age = 0;
setInterval(this.incAge, 1000, this);
}
Person.prototype.incAge = function personIncAge(that) {
that.age += 1;
};