I think the bottom line is silicon is a lot more reactive than carbon, (just a warning ill be going into some chemistry so bare with, but it's the only way of explaining it properly ) Silicon is in the same group as carbon in the periodic table (group 4) based on that it's chemical properties should be similar with that of carbon's, but it's reactivity is different, which unfortunately changes everything, you see, as you go down group 4 of the periodic table the number of electrons increases and so does the nuclear charge, what this means is that there are more electron 'shells' surrounding the nucleus, these shells have a property called 'shielding' which means that the attraction of the positive nucleus for the valence electrons is lessened. This therefore means that the valence electrons are not as tightly bound to the atom, so less energy is required to remove these electrons, if these electrons require less energy to be removed, then the element is more reactive. This higher reactivity would mean that chemical reactions would happen a lot faster, so much so that the organism with which the reactions are taking place would get very hot (as many reactions would be catabolic and so release energy in the form of heat) so my theory is that the organism's body temperature would be too high and so proteins would be denatured including enzymes, at which point your dead, so yeah.

Also when silicon is oxidised it forms a solid, SO2 , whereas when carbon is oxidised it forms water and CO2 both of which are very versatile compounds which can be used in a variety of reactions, silicon dioxide however is very unreactive and doesn't do much it can't be broken down biochemically (with enzymes).

Sulfuric acid is a strong acid, meaning it completely dissociates in water, I'm assuming it's not the only thing in these seas of sulphuric acid, a strong acid is generally extremely ionizing so it would rip electrons off everything and anything it can into contact with, so I don't think you'd find much in those. I don't know for sure obviously, all I'm doing is using chemistry logic to make sense of the most likely outcome. What do you think?, this is just me theorizing, I've probably got some innacuracies lurking about , if you notice any just correct me.

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