The init script is specific to Debian. I don't know what network-manager's stance is on init system support or even if they have one. I wasn't able to find one in a quick search.
Oh that's right, it does ask when you upgrade which script you'd like to use.... The package maintainers, yours and possibly the original one(?)... I can't for the life of me remember the options, but I know it usually asks which one you want between yours and the 'package maintainers version' every time you upgrade.
The init script is specific to Debian. I don't know what network-manager's stance is on init system support or even if they have one. I wasn't able to find one in a quick search.