> I find it amazing and worrisome that an object that size can get so close to Earth and hit Jupiter without astronomers learning about it until after the fact.
Amazing... maybe. But I wouldn't waste too much energy worrying about such an event.
> To me, it is an indication that current near-earth object surveillance systems are not worth much.
Correct. The effort is at an infantile stage.
Even if we knew a year ahead of an asteroid that was on target for the Earth, there's nothing in our current technological capabilities that could be done to divert the event. Our nuclear missiles weren't designed to go beyond Earth's gravitational pull, so they wouldn't be useful. And we most likely won't have a years warning; it'd be more like weeks if even that.
Some rough estimates put the number of asteroids in our own solar system to be about a billion. We're currently tracking an extremely small percentage of them; and that task is difficult enough as the asteroids make such infrequent appearances, and they're "small". But if even a small asteroid a few miles across in size traveling 60,000 miles/hr were to strike the Earth, it would drastically overshadow your bad hair day.
Bryson, Bill. A Short History of Nearly Everything.