Ok, a few things.
Nearly all small engines require Regular 87 octane. There are exceptions, but most small engines don't run a compression ratio higher than 9:1. Some can be as low as 6:1. Of course, combustion chamber design plays a major role in necessary octane rating, but in general small engines are not high performance machines and do not require high octane fuel.
The higher the octane, the slower the fuel burns, and the less heat produced. Fortunate, they formulate all gasoline grades to be within 2% energy content of each other. However, this is why you aren't supposed to run premium in an engine that only requires regular. It can cause carbon buildup with an engine that only sees light duty service.
Everyone has their things. Fill it up with whatever you want, it's not like he's going to know the difference. He probably uses Marvel Mystery Oil in the crankcase also. *shrug*
2001 Honda Insight 5MT, MIMA #163P - 158,388
miles and counting as of 7/2011
Best Trip - 82.0MPG over 1200 miles
2001 Honda Insight 5MT - 450,000
miles and counting as of 2/2012 (Fiancee's)
Best Trip - 92.4MPG over 400 miles
2000 Honda Insight 5MT, MIMA #173P, BCM Gauge, OBDIIC&C Gauge, Upgraded 8Ah battery - 227,248
miles and counting as of 10/2011
Best Trip - 83.1mpg over 458mi