Those whose primary expertise is in SQL Server appear to have the benefits and disadvantages of working in a single system. I know that this is a simplistic view but it does mean that the knowledge required is more clearly defined than some others and also it does tie them to a single product in the short term.

I am comparing this to application development where there are different application types; services, web services, web applications, desktop applications etc. With this comes the difficulties of a far wider range of possible technologies that means that there is less tie to the success or failure of a single product but, I would argue, more technologies to employ.

In some respects this can explain the depth of knowledge that DBAs can have whereas software developers often need a breadth of knowledge. Neither job or career is easier. Just different challenges.