A proper DMZ is still a valid concept, but was never that big of a deal. There are almost no resources that make sense to put there. If you have those resources, then sure. But who does? The advent of cloud computing, cheaper colocation, better IT knowledge, etc. has led most shops to not try to make "internal/external" shared resources where one side is public and the other uses LAN security; and what little of that remains in need is generally addressed with VLANs in a slightly different way.