Ammonia is antifreeze, that means it is useful in cold invironments like saturns moon Titan.
-180 makes Methane or water freeze, but Ammonia is able to make it fluent and suitable for life.
On the other hand, water is common in our universe, its from Hydrogen+Oxygen, that means you will find it everywhere. The chance life takes water instead of Ammonia as solvent is already bigger.
The next problem, Ammonia makes solvents fluent, but the temperatures stay the same (-180 on Titan), which is not suitable to life forms.
The rule is (at least for carbonlife), the hotter (unless it is too hot) the faster the reproducion and thus the faster the development of life.
And carbon, which is the construction of our DNA, doesn't harmonize with cold environments (from what i remember), silicon is better in cold.
But silicon is on the other hand not very good "constructor".
All in one, carbon is common (search: abundance of chemical elements), water is common, and thus life in warm environments (planet at 0.8 - 1.3 AU, in the case of yellow stars like our Sun) common.
While life on cold planets/moons, means far away from star and less photosynthesis
(but enough oxygen in the atmosphere of the Earth was the reason higher life (animals/plants) was possible, photosynthesis and enough oxygen is important),
ammonia not so common, siliconlife problematic (once, i heard a scientist saying, sex of siliconlife takes up billions of years

).
All in one, carbonlife in warm water is probably the most you will find.
http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry"