In addition to the other correct answers above, all the capture semantics aren't implemented by jQuery's own event system. It would be a lot of work and likely cause compatibility/performance issues. Also the jQuery special events hooks, which handle compatibility issues across browsers including the latest ones (not just old IE), only work for bubbling so that would need to be redone as well.
For example, if capture were possible and you run $("a").trigger("click") or $(".bar").trigger("myevent") there would need to be *two* passes through the DOM, one going down from document to the target for capturing and then the one bubbling back up as it does today.