AFMA is a product feature that Canon uses to convince buyers to move up to a more expensive model. If a ton of buyers sent their camera or lens in for warranty adjustment of the focus, they would add it to save themselves money. However, the kit lenses have a small aperture and larger depth of field, so focus errors are usually not a issue. Very few Rebel buyers buy expensive wide aperture lenses where any focus error really stands out.
Of course, there are some who do this, but few pay $800 for a camera and then buy $X,000 in lenses.
Its really no different from buying a automobile or a refrigerator, manufacturers add low cost features to differentiate more expensive models which often do not cost more to make, or the selling price is a lot higher than the cost of the features.
Its the way commerce works, the "UPSELL"