I saw that on the poll and though it weird too. Although I cannot remember the study, but it showed 25 faster than 23 but 28 about the same as 23.

I put the Bontrager 26mm tubeless on my flo wheels, and have been enjoying them.

My new Speed Concept even came with 25mm from the factory, so Trek has started shipping 25mm instead of 23mm with their tri bikes.