In the first case are they referring only to handedness in silanes, not oxides?
I'm honestly not sure. I do know that the microbiological selection process in early formation favored one "hand" of simple organics over the other and so all life on earth at the molecular level reflects this. From my limited understanding Carbon is the only element that exhibits this in a favorable way in regards to protein conformations.
Practically all the Si on earth is in the form of SiO4 tetrahedra linked in various ways. It's the same on the moon, Mars, and meteorites. None of these carbon-like silanes. Also Si has nothing analogous to CO2, whose soluble & gaseous state is so convenient for photosynthesis and respiration. SiO2 is a crystalline solid, almost insoluble.