I do web development and it's mostly the standard LAMP stack type stuff. One of the frustrations I have constantly is that I still need to learn how to do someone else's job simply to do my own.
In that regard I've learned how to use Linux with various services, learned about SOLR, Nginx, Apache, ESXi, Docker, MAAS, and a list of other things I've probably mostly forgotten. If I wanted to, I feel confident I could rebrand as a sysadmin, but lord knows I don't want to. I like writing code and solving challenges, but I hate having to trudge through all bits about getting infrastructure to work.
On top of that I work almost entirely on e-commerce sites, so I am forced to learn various business models, sales tax implications, PCI-compliance standards, payment and shipping APIs, assorted accounting software, and on and on.
I complain, but at the same time I understand that certain combinations of certain skillsets are what make an employee desirable. I like having the ability to do other people's jobs, sometimes I just don't want to.