articles - “the top levels of government” -- why not "of THE government"?

Example taken from: Russia questions five suspects over Nemtsov killing:

However no information has emerged as to the possible motive the men could have had in killing the charismatic opposition leader. His allies believe his assassination was a hit ordered by the top levels of government determined to silence dissenters. The allegation has been strenuously denied.

Why not say by the top levels of the government? What do you think the difference would be?

Answer

... ordered by the top levels of government ...

The "missing" article is called zero article:

Definition:

An occasion in speech or writing where a noun or noun phrase is not preceded by an article (a, an, or the).

In general, the zero article is used with proper nouns, mass nouns where the reference is indefinite, and plural count nouns where the reference is indefinite. Also, the zero article is generally used with means of transport ("by plane") and common expressions of time and place ("at midnight," "in jail")

1. 
   

   The indefinite article a (or its phonetic variant an) is used to indicate:

   
   

   
   
   

   
   
   • one of many -- I hope to meet a girl.
   
   
   • an unidentified thing (or person) -- I met a girl.
   
   

   
   

   
   


2. 
   

   The definite article the is used to indicate:

   
   

   
   

   
   
   
   • an identified thing -- I met a girl at the dance.
   
   

   
   

   
   


3. 
   

   The zero article is used to indicate:

   
   

   
   

   
   
   • generic plural nouns -- I have met girls in the past.
   
   
   • uncountable nouns -- I want to find companionship.
   
   
   
   • things in general -- The dance is at school.
   
   

   
   

   
   

It is quite normal for common nouns to use the zero article even in reference to a definite thing, especially as the object of prepositions. Everyone going to the dance knows exactly which school they will go to, but they have two options in talking about where the dance will be:

The dance is at school.
The dance is at the school.

Government is one of these common nouns that leaves the writer this option:

... ordered by the top levels of government
... ordered by the top levels of the government

One rationale for this flexibility is that the context already makes the identity of this common noun so definite that the definite article is implied even when it is not expressed.

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A partial list of common nouns that can sometimes be definite without the definite article:

Institutions: church, college, prison, school, university & hospital (except not hospital in US English) ... :

I met a girl at school, but not: I met a girl at dance.

Places: work, home, bed ... :
I met a girl at home.
but not:
I met a girl at dance.

Meals: breakfast, lunch, dinner ... :
I met a girl after dinner.
but not:
I met a girl after dance.

Holidays: Christmas, Easter, Hanukah, New Year ... : I met a girl after dinner.

but not:
I met a girl after dance.

Transportation: bike, car, foot, plane, train ... :
I met a girl on foot.
but not:
I met a girl on dance floor.

For more detailed information consult:

http://en.wikipedia.org/wiki/Zero-marking_in_English#Zero_article

http://grammar.ccc.commnet.edu/grammar/determiners/determiners.htm