Object-orientation isn't a language feature, it's a programmer feature.
C is a useful lowest-common-denominator language which can be accessed from anywhere. It also tends to be more efficient than the alternatives. That makes it useful for writing truly common libraries.
Now, having said that... I don't know whether C is the best language to write a network-manager-like program. I'm partial to wicd myself, which is written in Python. As long as the DBUS bindings can be accessed from any language, the choice of implementation language seems irrelevant.
And now it's time for a language flamewar, where all the usual points will be brought up exactly as usual. Move along, nothing to see here.