Segregation of Duties related

[Faheem SIDDIQUI <fahimdxb () gmail com>]

I am preparing a "Segregation fo Duties` Matrix within my IS function 
(Is there a better way to hit it?)

I found a very basic chart at ISACA website: ( Linked Below...)

According to this chart, some of the things in the Control Matrix are 
obvious but some aren`t so.

A few that I am having difficulty understanding are: For example, A 
database admin can be a 'Tape Librarian' but Network/Systems admin 
create a control weakness on this job function and so does a Security 
Admin. Why?

-> Also, DBA can be a systems analyst but cannot be an application 
programmer.
-> A Network or a System Administrator, cannot be a Help Desk Support 
manager.

I was wondering, what are the potential control weaknesses here??
The information I am referring to can be found at:

http://www.isaca.org/Content/ContentGroups/Certification3/CRM_Segregation_of_Duties.pdf