Author's claim that chain checkers are innacurate is based on the assumption that roller wear is not relevant; and thus adds innacuracy to checkers which measure based on roller position.
On what do we base the assumption that roller wear is not relevant?

Seeing as how the rollers are the primary(only) interface between the chain and the sprokets, I suggest that roller wear is in fact quite important, and that there is nothing wrong with chain checkers which use the rollers as their contact points.
In fact, they take into account wear which a ruler measuring the pins from an external-only view does not.