When you start your career as a systems administrator you need to be a generalist. This might mean knowing about several operating systems such as Windows, Linux or Novell. You might even have a bit of routing and switching knowledge from one of Cisco’s certifications.
As you progress in your career, you will need to become more specific with your knowledge. A generalist has shallow knowledge of many topics. A specialist has deep knowledge of a significantly smaller number of topics.
The reason for this is simple. It takes time to develop a deeper understanding of a topic. What you are fighting against is that knowledge in IT is very transient – what is useful to know today will most likely useless to know in ten years time. Back in 1994, I was pretty deft at configuring Windows 3.11 boxes to work with Banyan Vines. Today that knowledge is almost useless to me.
Whereas it might only take a few weeks to pick up a generalist understanding of a topic, it might take a few years to gain a deep understanding of the same topic. It is the people with the deep understandings who can command a higher wage. Someone with only enough knowledge of Active Directory to pass the 70-294 exam isn’t going to command the wage of an Active Directory specialist who might get to consult on very large projects.
Where this is all going is that a few years after you got your first sets of certifications, you should know enough about what interests you to be heading down a more specialized path. You might start of with an MCSA and a Linux+, but five years down the track you are likely to have a specialized understanding of Windows or Linux, but unlikely to need a specialized understanding of both for your job.