It doesn't model everything. They tried to use GR and RET astronomy to model the movements of the stars and galaxies and failed utterly.
No, they don't utterly fail. GR passes many amazing tests. See: http://en.wikipedia.org/wiki/Tests_of_general_relativity
Except the test of applying to the actual universe.
Really? Are you claiming the experiment showing the predicted procession of the aphelion of the Mercury was not in the actual Universe?
If you manage to fit General Relativity up to explain the precision of Mercury, those equations you used can't be used predict the precision or aphelions of stars or galaxies. You took a puzzle piece and were able to fit one piece into a slot on the board, but in doing so the three other slots on that piece do not fit. It screams failure.
It was more to explain the distribution of galaxies and the increasing rate of expansion of the universe, but meh. You tend to misrepresent and misinterpret science as it suits you.
Actually, they can't even use GR to explain very simple things like the spinning movement of galaxies. Galaxies are observed to spin as if they were solid disks, but according to theory, the center of the galaxy should be spinning much faster than the edges. In order to explain the rotation of galaxies they need the entire galaxy filled with some kind of substance which holds the stars strongly together.
See
http://news.softpedia.com/news/Stars-escaping-out-of-the-Galaxy-17222.shtml"According to theory, a galaxy should rotate faster at the center than at the edges. This is similar to how an ice-skater rotates: when she extends her arms she moves more slowly, when she either extends her arms above her head or keeps them close to the body she starts to rotate more rapidly. Taking into consideration how gravitation connects the stars in the galaxy the predicted result is that average orbital speed of a star at a specified distance away from the center would decrease inversely with the square root of the radius of the orbit (the dashed line, A, in figure below). However observations show that the galaxy rotates as if it is a solid disk as if stars are much more strongly connected to each other (the solid line, B, in the figure below)."
Considering the success of GR to this point, which is astounding
I would hardly call a theory for gravity which needs 96 percent of the universe filled with undiscovered and undetectable dark matter and dark energy "astounding". Well, I would. But not in the way you intended.
No, pebbles are not "flawlessly smooth".
They are certainly much smoother than the boulders we have been shown in this thread.
Also, are you suggesting that all pebbles are exactly the same size, or do you admit that pebbles can come in various sizes?
The stones in that picture seem to be a mixture of cobbles and pebbles. Pebbles will never be over 64 mm or under 2 mm.