That "air-space" is there for a reason and is an integral component of the masonry structure. It (the space) creates a thermal barrier and also allows any moisture that gets through the mortar to dry properly. To inject those spaces with foam would only be the beginning of the end for the exterior structure. The foam will hold migrating moisture and if you are in a winter-freeze area expansion from freezing will eventually demolish the masonry wall for you.
For some one to claim they have filled that 1" space and noticed a difference is just plain baloney. They are just trying to justify a bad decision.
As you said...the only people recommending the procedure are the people selling the product to perform the procedure. I would leave it alone.