That's again a myth. There is no dbus dependency. You can use dbus to do activation but you don't have to. Now, there is a dependency on libdbus which just means systemd is using the dbus serialisation format for its ipc (which, I repeat, don't have to happen over dbus).
It's because I'm not really precise (but neither is Lennart). Technically, libdbus is a part of dbus. It allows two applications to communicate with each other using the dbus serialisation and abstracts the transport layer. You can use it over a Unix socket and then it's just a serialisation format like any application using IPC would need. Then, using dbus is no more stupid than anything else. Actually, it's pretty clever as there already is quite a lot of tools understanding this format.
However, libdus is not what people usually talk about when they talk of dbus. The core part of dbus and what could bother server administrator is the message bus daemon which allows any applications to expose their functionalities and talk to any others. Now, systemd can use the message bus to allow applications to ask for service activation. But, it's not required and you can run the init system without it.
