However, I have seen plenty of example where that is not true.
Enterprise databases are a great example. While the DBA can often do alot to compensate for dev's bad db code
A fulltime employee can work on optimizing code for an entire year before it pays to add another node to the cluster. (server hardware, hba's, fiber switch ports and most importantly oracle licenses). Interestingly enough PHB's often times choose expanding the infrastructure eventhough the ROI is not there citing opportunity cost, etc.
Another favorite are processes running on new hardware
From my experience most of these issues dont go away by horizontally scaling and eventually they come back to haunt you one way or another.
Surprisingly, the added cost of administrating added infrastructure is never part of the calculation