Pakistan should talk of accepting apology if they provide compensation of all the damages NATO has done, infrastructure and human lives. And ask them to stop drone attacks and instead give the location of suspected terrorists to Pak army to take action. Toll charges should also be asked to pay. Until these demands are fulfilled, no apology acceptance, no supply opening.
A formal apology changes everything for the simple reason an apology is only issued when there is confirmation of fault from them. An apology confirms it was their fault and nobody else - so not only are they liable for what happened - they cant hold and declare the moral ground. Lovers of the USA will find it difficult to accept that their moronic chaps were responsible for such an hideous act. So many i have heard idiots say "lets wait and see" - well a formal apology will be confirmation of fault and an acceptance of liability.