If Einstein explained in the General Theory of Relativity that
gravitation is caused by the curvature of spacetime rather than the
force of gravity then why do scientists still count gravity as one of
the 4 fundamental forces of the universe?

miles
          it is not 'either or' one RATHER THAN the other, as in

 as  in "curvature of spacetime rather than the force of gravity"

   Einstein pioneered 'geometrisation of physics' -
 he has shown that abstract geometries  
http://www.maths.gla.ac.uk/~wws/cabripages/klein/klein0.html

can be used as a language for physical theories.

 So, his General Theory of Relativity (GTR) is still a theory of gravity,
 and his theory of gravity is reduced to Newton's theory when v/c <<1.
 

advanced links:
 " Geometry and modern cutting-edge Science More than two thousand
years ago, Plato, with a leap of the imagination had remarked: "The
Gods ever geometrize." Physicists have now given rigorous proof that
Plato was indeed right. We have now reached a stage where Physics and
Biology have both been geometrized. Through explaining gravity as
curvature of space-time Einstein's General Relativity initiated the
geometrization of Physics. More recently the work of Professor Myron
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http://www.mumfordbooks.co.uk/CAT.asp?CatID=38


abstract geometries:
http://en.wikipedia.org/wiki/Non-Euclidean_geometry
http://en.wikipedia.org/wiki/Riemannian_geometry

When they refer to "The Forces", they mean rather generally "The
Interactions". In modern theory, everything has been *reduced*,
supposedly, to a manageably small menu of redundant objects & their
modes of interaction. One such mode is gravitation between regions of
space filled with momentum-energy, i.e., "mass". A region containing
mass induces curvature locally. The curvature of one locality
determines the curvature of adjacent localities, extending outward
radially from the concentration of mass.

   Actually, there's energy, -mass-, in each infinitesimal locality,
thus its curvature, and thus that tiny region interacts with the
neighboring regions, endowing them with potential energy: their
curvatures.

   As you appear to understand, general relativity models gravity
rather differently from the other thoroughly quantum mechanical
interactions. But nevertheless, gravity is (so far) an irreducible
player in the big chess game called The Universe, and so it is one of
the "forces".

It should be noted that GR is effectively equivalent to Newton's law
not just when v ~ 0. It's also necessary for the local curvature to be
~ 0, and, just as importantly, for the radius between gravitating
objects to be ~ 0.

   The reason for the distance condition is that, in Newton's theory,
there's a tacit assumption of interaction across arbitrarily large
distance with zero delay time ("instantaneous action at a distance").
GR, on the other hand, is characteristically local in all
interactions, -there is no gravitational interaction between Earth &
the Moon; there is only motion determined by curvature exactly where
either body happens to be- and disturbances in the field propagate at
a finite speed. For Einstein's & Newton's laws to tend to generate
precisely the same numbers out to the nth decimal place, they must
deal with homogenous, empty space.