BIND from system and from ports

[Eir Nym]

All is good in BIND in system, except it depends on ports tree with
various options.
I have to do followed algorithm, to enable these options:
1) make and install base system
2) install needed dependencies from ports tree
3) rebuild and reinstall world

This is more complex than:
1) make and install base system
2) install same(?) BIND from ports tree with same options

Why does base system has any dependencies from ports?
I know about application features, but special cases aren't special
enough to break the rules, isn't it?