Thank you.
The OP is asking for comment about a statement from a friend that has lived in Hawai`i for 10 years, so I commented based on that, and the perception from Hawai`i.
As Melissa stated, its what is available, and right now, the 4 major companies - Kamaka, KoAloha, Kanile`a and G-String - simply build what moves, Koa. Personally, I've built 3 all Hogs, and 3 all Koa, so I'm running 50%, which is REALLY high for Hogs, but my numbers don't make a dent and shouldn't be counted.
I should define a little more to avoid a misleading statement from me: In "general", the hogs in Hawai`i are found on cheaper instruments, or Martins, or customs. Spruce will be the same, cheaper instruments (even Oscar Schmidts included as an instrument), or Customs. Midrange Factory Instruments from Kamaka, KoAloha, Kanilea and G-String are Koa - let's just call Ko`olau a high end Factory instrument.
Note: most `ukulele players, here, are not guitar transfers. Most `ukulele players, here, start as `ukulele players, as a kid. And they move towards Spruce tops more than likely as an upgrade (because now they have a custom), or add on to the arsenal.
-Aaron