But there are real reasons to suspect that it's likely. Some atoms are more common than others. In general, light atoms are more common than heavy atoms. Life is going to use the tools which are commonly available on its planet, so life that has uranium as a basic constituent of their biochemistry would have to come from somewhere quite strange.
And you can also rank the atoms by how many different types of bonds they can form with other atoms. Noble gasses form almost no bonds at all, with anything, so it seems pretty unlikely that any form of life would use them. Carbon and oxygen, and the other atoms in those columns of the periodic table, form lots of types of bonds and can do so with several other atoms at the same time. This gives you lots of complex molecules.
Carbon and oxygen are in the sweet-spot, and therefore it seems likely that alien biochemistries will use them. Of course, the set of chemicals that you can make with with them is quite vast; it's also likely that an alien biochemistry would have only the simplest and most basic molecules with ours, even if it's based on carbon and oxygen. Luckily water is quite a simple molecule.