From any point of reference the sun is the centre of this solar system and everything in this system orbits the sun.
Not at all. Nothing orbits the sun. The planets and the sun all orbit the barycenter of Sol System, which happens to almost coincide with the center of the Sun. See, e.g.: http://en.wikipedia.org/wiki/B...
Anyway, the claim that "from any point of reference the sun is the centre of this solar system" is just wrong. Walk out your front door on a clear night and you can watch the planets and stars rotate around you. You're the center, from that particular frame of reference. Sure, to describe the motions of the planets accurately requires an absurdly complex set of epicycles, so complex that they cannot be evaluated without the use of computers... but you can do it: the math gives equivalent results. The math may be easier in one reference frame, but that doesn't make one reference frame more correct.
Here's another example: stand still and spin around really fast. Your arms will naturally lift and move outwards. In one frame of reference, you're spinning and centrifugal forces are lifting your arms up. In another frame of reference, you're standing still and the entire universe has started spinning around you, and the tidal forces generated by that much mass (at, admittedly, that great a distance) generate a pull on your arms that lift them up.
That may sound pretty out there, and it is -- it was one of the arguments Kurt Goedel used against relativity back in the early 20th century. ("That's all well and good, Einstein, but if there's no preferred reference frame then how do you account for this?") Then Goedel sat down with the math, crunched a ridiculous lot of numbers, and discovered that yes, General Relativity gave the exact same results as classical physics.
We may want to choose one reference frame or another to make the math easier -- but that doesn't make one reference frame more correct than another.