TSA allows knives on planes, flight attendants union calls decision 'dangerous'

With other precautions that have been put in place since 9/11, such as continually locked and reinforced cockpit doors, what makes an airliner terribly different than a bus, or even the counter lines at the airport? Is someone able to wreak more havoc with a pocket knife or a bottle of shampoo on an airliner that they couldn't elsewhere?

Somewhat. But you are isolated while in flight with landing time usually a 1/2 hour or more away. Unlike a bus that just stops in the street or pulls over if there is an incident.

Somewhat if an interesting statement...

"Sharp objects can no longer bring down aircraft, former Transportation Security Administration chief Kip Hawley told CNN,.."

no longer? Since when could they?