The liquids and bottle issue was a reaction to an actual terror plot. They were planning to build a chemical bomb on the aircraft after bringing the components in separate containers.
They actually arrested a young mother who was to carry a chemical component in her own child's baby bottle. The child was to be on the flight.
This is why we should error on the side of caution.
And if you had followed the story closely, you would have discovered that the plot was uncovered not because they were checking shampoo at the airport, but because good investigative work had uncovered the plot in the first place alerting them to the problem.
It is the difference of doing investigative work to find Mohammed Atta's or looking for the next subsitute for a box cutter in passengers luggage.