The parts of a research article includes an abstract, introduction,
lit review, hypothesis, methods, results, discussion, and references. 
Why is this so ?  Why does it have this particular outline ?

The exact format that is used in a research article can vary,
depending upon the specifications and requirements of the publishing
entity. Such an article is typically written in such a manner as to be
acceptable to the journal to which it is submitted.

Parts of a scientific article depend on particular discipline
(inorganic chemistry, quantum physics, etc) and a type of the article
(communication, full paper, review etc). It doesn't depend very much
on the publishing entity, as most peer reviewed journal of the same
discipline have similar, and often identical specs and requirements.
For example, a full paper in chemistry would normally be required to
have: graphic for table of contents, abstract, introduction,
experimental part, results, discussion, references.

Often results and discussion are combined into the same part, "results
and discussion", and is either way is permitted in all chemistry
journals.

The comments by acrh2-ga are quite correct. The discipline and type of
article are more important in dictating form than the actual
publishing entity.

In general, scientific papers all follow this general outline for
simple and practical reasons.  The previous comments point out various
modifications to the outline presented in the question without actually
providing an answer.

Scientific reports follow this general format to provide information about
the paper's potential relevance to other researchers as quickly as possible.
The papers are generally intended for a specialized audience of people
who understand that the paper in question addresses a very specific
experiment
that may or may not be important to the reader.  The reader initially wants
to know whether he or she cares to read beyond the first few lines!  If it
looks interesting, they'll read the whole thing.  The generic outline
is designed to make it simple to extract this information as quickly
as possible by presenting everything in a standard way.

Coming first, the abstract is short, contains the hypothesis and the
result, and is often the only thing people read (along with the
title).  Abstracts are
also the only part of the paper intered into electronically-searchable 
databases. Once the reader has decided he wants more, the paper provides the 
general background for the research question (introduction) and what similar 
work has been done in the past (lit review). At this point, the reader should 
understand WHY a new experiment was required, so the outline now moves
on to the current results.

To describe the new research, the author first indicates exactly what the new 
experiment was designed to answer (hypothesis) and how this experiment
was carried out (methods).  Once you know how it was done, it is
logical to
explain exactly what you saw (results) and how this should be 
interpreted (conclusions).  Along the way, the author has usually
indicated previously reported results; these are traditionally placed
at the end so
they are easy to find.  The older "footnote" convention from printed
books could have been adopted, but most journals just stick them all at the
end.

The outline is often explicitely included in many journals by including
headings for the sections (Introduction, Results, etc.)  Most people only
look at the part they care about, reading the whole paper only if they
need to.  For example, if all you care about is whether your competitor
acknowledged what you recently did, you'd just jump to the References
section!  The standard outline (with slight modifications from journal
to journal) always lets you jump to the part you're interested in quickly.