They are being very conservative in that NOTE, probably because it's cheaper than actually doing the flight test, AND because pilot technique introduces some variation.
Think of it this way: On a rolling takeoff, at the point takeoff power is reached, you've already gained 30-40 kt. speed. On a static runup, the equivalent point is ZERO kt. Applying the above NOTE, actual performance will be BETTER than a static TO.
(PS: on the SE overpowered taildragger I'm used to flying, running up to TO power then releasing the brakes is a sure recipe for a groundloop - assuming you didn't dig the nose in first!
)