Well no kidding there linked in some fashion, the header of the paragraph is "Octane Recommendations", which is providing 4 individual recommendations/warnings related to octane. Anyways, interpret how you please.The last sentence is related to the others because it is part of the same paragraph, that is english grammar. If that sentence was not related it would be part of another paragraph.
The way an engine is tune has more to do with the octane requirement than the compression ration does. A 12:1 carbureted engine can be tune to run on 87, it won't make near as much power as if it were tuned to run 87 due to the ignition advance you would be limited to. DI engines are quite different when tuning because all the benefits it provides, such as better atomization which leads into better air charge cooling and so on and so on. Needless to say you can run more aggressive tunes with lower octane fuels on a DI engine vs their convention fuel injected counterparts.The manual is clear. Premium improves performance. Manual notwithstanding, it stands to reason that higher octane is beneficial for a car with 12 to 1 compression. There are two questions the manual and common automotive sense don't answer. First, does premium solve any of the complaints like shuddering? Some on this forum have reported that it does. I use premium and have had no shuddering or other issues. Second, is the added cost worth it? I doubt premium's added cost is worth the performance gains or MPG gain (if any -- regular may give better MPG).
So as I see it, premium is worth a try if you've had shuddering or other performance issues, or if you're a leadfoot who wants to see whether there is a power improvement.
Once I have about 4k miles, I intend to switch off premium to see how regular compares in the fuel economy department as that is my principal concern.