Javascript event handling (all browsers except ie7)

Now that IE9 supports addEventListener and IE7's market share is diminishing (goodle analytics tell me that ie7 and older is at 14% and loses 2% per month).

If we can support ie8 (@31%) we can forever forget attachEvent.
That mean we support all current browsers but not ie7 and older.
ie8.js:

/*@cc_on
  @if (@_jscript_version >= 9)     // >ie9=========================================
  @elif (@_jscript_version == 5.8) // ie8=========================================

if (!document.addEventListener && document.attachEvent){
    HTMLDocument.prototype.addEventListener =
    Element.prototype.addEventListener =
    Window.prototype.addEventListener = function (type, fCallback, capture) {
        var sEvent = "on" + type;
        if (capture) {
            throw new Error("IE does not support capture");
        }
        var that = this;
        this.attachEvent(sEvent, function (e) {
            Object.defineProperty(e, 'currentTarget', {
                get: function () { return that; }
            });
            Object.defineProperty(e, 'eventPhase', {
                get: function () {
                    return (e.srcElement == that) ? 2 : 3; // "AT_TARGET" = 2, "BUBBLING_PHASE" = 3
                }
            });
            var time = new Date();
            Object.defineProperty(e, 'timeStamp', {
                get: function () { return time; }
            });
            fCallback.call(that, e);
        });
    };
    Object.defineProperty(Event.prototype, 'target', {
        get: function () {return this.srcElement;}
    });
    Event.prototype.stopPropagation = function () {this.cancelBubble = true;};
    Event.prototype.preventDefault = function () {this.returnValue = false;};

    HTMLDocument.prototype.removeEventListener =
    Element.prototype.removeEventListener =
    Window.prototype.removeEventListener = function (type, fCallback) {
        this.detachEvent("on"+type,fCallback);
    };
}

  //@elif (@_jscript_version == 5.7 && window.XMLHttpRequest) //ie7
  @else        //ie older =================================================
    alert("This version of IE is not supported! Use at least:\n"+
    "IE 8.0\n"+"Firefox 4\n"+"Chrome 6.0\n"+"Opera 10\n"+"Safari 4");
  @end
@*/