I think you will find that the 'blocking in' is more symbolic than anything. Immobilising the asset for legal purposes as aircraft are considered to be mobile assets and there are also obviously laws concerning interference with a moving aircraft.
That's an interesting point for debate. If an airline was to obtain clearances from air traffic control and begin to move an aircraft, could a third party or the airport operator lawfully stop the plane taking off? There are some bits and pieces of aviation law in there which could be open to interpretation.