Being a SQL Server guy, you can be a pure SQL Server Developer, SQL Developer DBA, SQL Production DBA, BI developer or the Generalist DBA. The Generalist DBA needs to do anything and everything about SQL Server. In the current IT world , a DBA needs to have some knowledge about Windows, Networking, SAN etc.
My career started with me being a Generalist DBA who needs to just know the basic administration stuffs and then graduated to be an expert. Working for few years as an expert in some of the areas of SQL Server made me realize that I am good in some bits but don’t have a clue of lot of bits in SQL Server. While I was able to resolve some rare performance issues or clustering issues or SQL Server Setups I was not able to develop an SSIS Package nor deploy a report in reports server or do a bit of programming. Needless to mention the fact that I used to have goosebumps when I need to collaborate with the network/SAN/Windows guys as it was hard for me to understand what they really meant. I always thought anything other than SQL Server Engine is not something really great to work on.
A further career move made me realize the importance of understanding all the relevant aspects of SQL Server and all relevant things that hold SQL Server up be it networking, windows, SAN etc.
While it is really important for one to be a Master in some fields to grow in his career, it is also extremely important that he knows all the other related aspects. I strongly believe that you cannot be a Master in SQL unless you are a Jack of All trades though you believe you are a Master.
From what I have experienced, Your should be a JACK of All Trades and a MASTER of SOME . I hope I would soon become that and I very well know I have miles to go before I sleep and then I can dream of being a MASTER OF ALL TRADES !!