Deputization/Police not obligated to help

I came across this article this morning:

http://www.disinfo.com/2010/03/the-police-arent-legally-obligated-to-protect-you/

I did not know this before this morning, however, it is my understanding that the police/sheriff’s department are fully entitled to obligate(deputize) me to help them.

They don’t have to help me, but I have to help them? How is this possible? What is the reasoning for this?