If the asteroid had impacted at sea (most likely), the tsunami (tidal wave) would have devastated all its coastline. If the impact had happened on land, you can bet that jumpy governments would have thought it was the first nuke of WWIII. In any case, the disaster would be so great that all others would pale in comparison.
Do you realize that there are more people working in your neighborhood retail emporium than are watching the skies for Near Earth Objects right now? Oh, and that's the Northern Hemisphere only. Currently there is no dedicated Southern Hemisphere NEO program.
That's like only scraping the ice off half your car's windshield. You can see to drive, but what might be coming from the direction you can't see?
This is the kind of impact crater you get from an object only 100-150 feet in diameter:
Barringer Crater in Arizona is nearly a mile wide and 570 feet deep.
