It is a lot easier to make an argument for inorganic methane than it is for inorganic oil. Inorganic methane as both you and I pointed out, exists both in the atmospheres of the gas giants and in vast pools on Titan. Since methane exists where there is no life, there must be some inorganic process to create it. You either have to prove life exists on Titan, which would in and of itself be seriously cool (OK on that mood seriously cold), or there is an inorganic source for the vast amounts of methane.
Likewise last year measurable amounts of methane has been found in the atmosphere of Mars. Methane breaks down in ultraviolet light from the sun in less than a year, so scientists know it is being replenished in some way from the planet itself. There are only two options, either there was life on Mars, or there is an inorganic source of methane. It has to be one of the two and either one is an awesome discovery.
Methane concentrations on Mars
Unfortunately no such proof exists for the complex hydrocarbons like oil. As was pointed out earlier complex hydrocarbons break down into methane. But going the other way is a lot harder. Not impossible, but a lot harder.
I know that absence of proof is not proof of absence. But that has always been a cop out argument. We have yet to find oil on Earth or anyplace else that is clearly inorganic. That doesn't mean it is not possible, but if it is a common occurrence we should be finding more. If it is possible, but uncommon, it doesn't change the math enough to matter except as a scientific curiosity.