It would be somewhat OK (not acceptable, though) if it were only for racing tires, which is where all this started (AFAIK). Manufacturers wanted to have the lightest tire at a listed size, so they were over-marking tires: A 24 marked as a 25, etc. Now it seems that's the standard, even for tires where weight doesn't matter for squat, like a puncture resistant commuter/touring 35mm that actually ends up at 32mm on the rim. Ooooh, it's 25g lighter than the other guy's tires. Big whoop.

And let's not get started with clothiers and arbitrary measurements. An inch isn't an inch when talking about clothing these days...