With regard to who pays for what, the original GHA was often between two airlines who carried out reciprocal handling at each others airports of operation, therefore it was felt to be sensible to have a hold harmless clause rather than two law suits with only the lawyers getting rich.
However with the rise of the independent ground handler the airlines thought that it would be better to have the option to recoup costs from them when an accident/incident was caused by their staff. Therefore the SGHA was amended in 1998 I think, and airlines were given the option of taking the Clause 8 Hold Harmless out of their agreement.
The Grnd Handlers were then exposed to a greater risk and their insurers sought an increase in the insurance premiums. The rise was not small as you might imagine. The Grnd Handlers, unsurprisingly, have little option other than to adjust their handling charges to any airline that wishes to opt out of Clause 8.
The airlines when presented with this potential significant hike to their handling fees have by and large taken the view that ground handling damage is a rarity over a year on a flights operated v damage comparison. Consequently very few opted out of Clause 8, and negotiaition on the basis of good will, future business etc is used when extreme cases happen as in this instance.
Tech question to those who know more than me about a/c systems. Articulated lorries have a system that allows the tractor unit to apply the brakes on the following trailer at the same time that the driver applies the brakes in the tractor cab, as do car/caravan combos. Would it be possible for a system to be designed that would allow the tug to apply the aircraft brakes in a similar way? or maybe some external clip/bolt on that is attached prior to every tow and removed at the completion?
Just a thought.