That's pretty silly. What "shared resources" am I contending with previous developers for? It's not like "oops, I can't deploy to the QA environment now, it's in use by somebody who left in 2015"

Also all the remedies he suggests (keeping your responsibility assignment matrix small) would make absolutely no sense if "communication costs" was dominated by the cost of communicating with developers in the past. By any reasonable reading communication costs refers to developers simultaneously working on a task (in analogy to parallel processes).