Also they don't add an empty rule for the source file (like they can do for headers), so if you rename from e.g. foo.c to foo.cpp, which still produces a foo.o, your incremental build fails because the dep file still has the dep on foo.c which doesn't exist anymore.
The original sin here is generating the dependencies from the source files in the same step that was used to generate the object files. The only way to ensure that Make observes structural changes in the dependency DAG is if the graph is rebuilt.
