The international agreed-upon limit is 12 miles. China claims 200 miles.An apology for being where we had every right to be would be seen as tacit agreement to the 200 mile claim. Regardless of the circumstances and any future repudiation of the apology it would set a precident that could cause lots of problems later.
As far as "sovereign territory" goes, I believe that there is an international agreement that any plane in distress can land anywhere it needs to and that it shall be treated as sovereign territory and all assistance to get it home safely shall be rendered. I'll try to find the reference but it has been 10 days.
China's premier has had to deal with his countrymen and the hawkish Peoples Liberation Army. In order to maintain his power base, he had to do a lot of careful juggling and diplomatic face-saving. These things take time. You will note that there were no massive demonstrations like there were when the Embassy was bombed. No one wanted a crisis. Bush managed to curb his natural impatience and the deal finally went through.troll