Hello.
I write most apps as paid and ad supported (AdMob) free version.
The pain of going through the process of manually editing manifest file, making it read only, checking "do not overwrite..", recompiling etc etc is error prone (as in don't forget to do it) every time I release an update, could be eliminated if the necessary code could be inserted into the manifest when AdMob library is selected/used in the project.
I remember EREL saying that the xml file has a template, so if you do use admob in most of your apps, then just edit the template and you don't have to worry about it again...