I've heard this kind of expression differently formulated (I think often by Steven Sinofsky while he was the head of Windows) as the complexity of the software

I've heard this kind of expression differently formulated (I think often by Steven Sinofsky while he was the head of Windows) as the complexity of the software unavoidably increasing quadratically with either time or with feature-count. So maybe it's less about the # of systems here specifically, more about just the # of "things it does", where most of what it does is connect systems together.