I do Starling.multitouchEnabled = true in my Main class.
Then later:
starling = new Starling( ViewStarling, stage, null, stage.stage3Ds[0] );
starling.start();
var gesturesManager:IGesturesManager = GesturesManager.getInstance();
gesturesManager.addDisplayListAdapter( starling.display.DisplayObject, new StarlingDisplayListAdapter());
gesturesManager.addInputAdapter( new StarlingInputAdapter( Starling.current ));
Then in StarlingInputAdapter, I've added some outputs to supportsTouchEvents function:
trace( "Mouse.supportsCursor", Mouse.supportsCursor ); // true
trace( "Starling.multitouchEnabled", Starling.multitouchEnabled ); // true
trace( "supportsTouchEvents", !(Mouse.supportsCursor || !Starling.multitouchEnabled) ); // false