Take it for what it's worth. I stopped caring what people think about me a long time ago.
I'm not singling you out, so please don't be defensive. I try to educate people, so for the handful of folks that will actually read this post, think about what I'm about to tell you. Your tuner tells you he'll give you an "auto-tune". Then he provides a flex-fuel sensor with a cool app that will tell you your ethanol percentage which you'll also probably pay for him to install on a non-flex fuel sensor vehicle. So now you can tell how much ethanol you're running. And how does the ECU know? Wait, you mean because it isn't a flex fuel sensor equipped vehicle there's no extra wiring harness wires? Which means there isn't any way for the ECU to "see" WTF the sensor is outputting, let alone allow a tuner to adjust some "map" for a sensor that doesn't exist?
The truth is, that the ST and other non- flex fuel sensor vehicles ECU is using the wide-band 02 sensors (there are other patents on using vapor pressure) to "estimate" the ethanol content. That allows it to correct for fueling and some ECUs will try to use this info to adjust the ignition timing to take advantage of this so MPG doesn't drop as much as it might otherwise. But it sure isn't automatically creating a real-time tune that adds 100 plus HP. If that was the case, you wouldn't see a good tuner adding 100HP on just a 93 tune, nor would we need a tuner. But performing a bit of adjustment is totally within the stock ECU capability, and a tuner might even be able to take advantage of a fuel correction map to adjust timing to make changes. But that "auto tune" is built into the algorithms of the ECU, not some genius "tuner", especially in the case of a supercharged engine (like the CTS-V) where it's impossible for the boost to adjust (outside of changing pulleys).
No matter what ECU you have, a great tuner is playing with the boost (via the wastegates), the timing, the cam phasers, and experience to get the most out of a particular engine based on the fuel you specify. If someone's trying to sell you a flex fuel sensor for a vehicle that doesn't come with one and telling you it's going to magically adjust timing, boost, and cam phasing- well they're playing you.