One can configure an HP Z840 workstation with 2TB of RAM and 44 cores. The vast majority of developers can and do work with much less. The question is, what are the true power users using?
If they are all developing with Xcode I bet they also have a server farm for distributed builds. That said, why would OSX devs need more that 16GB of RAM? It's not like they are going to be running virtual machines/docker images. Xcode isn't _that_ much of a memory hog.