I understand that ignition timings change with different combustion variables in fuel - but that's all the article says. There are no dyno-graphs with varying grades of fuel in the same car under controlled conditions in that link at all.
My argument isn't that torque or bhp isn't increased necessarily, just that the increase is actually noticeable. I don't think it is. To 'feel' a performance increase you'd need to be running a car with 400bhp + that actually relies on having proper fuel put in it.. and even then.. when you've got that amount of power under your foot, the 30bhp or so difference is really nothing at all.
And on the subject of 'feeling the difference', even a 10bhp difference would barely be noticeable in a 200bhp car, where as it's a very well documented fact that if someone does something to their car which they're told will boost performance, they will feel that even if it's not really there. Scammers on ebay feed off this type of delusion with their 'electric superchargers' and 'ignition timing advancing diodes' etc.