Part of the problem is in how technologists categorize skills. I used to explain to my development staff that you are not a particular type of programmer. You are not defined by the tool but by what you produce.
In truth, most technologies share common elements, with the differences largely being semantic and logistic. But the core implementation of one technology is, in fact, quite similar with that of another related technology.
Here's an example to illustrate. Numerous Novell engineers were left behind upon the emerging market dominance of Windows NT. They felt that they didn't have the time to learn Windows NT while supporting and developing their current NetWare environments.
However, technologists who understood that the differences between the two operating systems were not so great quickly added Windows NT skills. In fact, they understand that whether it is NetWare, NT, Banyan Vines, or some other network operating system, notable similarities made the technology philosophically similar.
In their core utilization, the network operating systems mentioned are still simply methods for the storage, retrieval, or integration of data and applications. In each, you had users, groups of users, protocols, and connectivity.
I am purposely oversimplifying the idea to make the point. The fact is that many technologists who were more conceptual in their approach made the transition with little or no training. They understand how to study and adopt new technology quickly and without panic, as described in the section that follows.