They only lean toward MAC/IP topologies in BPL. In lower-bandwidth scenarios (metering) they go a variety of ways, largely because extended distances mean signals from a given node won't be visible across the entire network, which forces a repeater mechanism of some kind. It gets complex fairly quickly, especially in commercial systems, where huge banks of fluorescent lights create some unpredictable behavior.
Making things worse are the customers who have heard about BPL and say, "Why can't you just replace all these devices with something that does broadband and greater throughput?"
