My experience with process automation tells me it's true.
Yes - there is a distincion in putting parts of different quality on different markets and probably for different models. But usually it is with the same parts, meant to be made to the same specs. Problem is - production process isn't always perfect and occasionally some products don't pass the entire quality control process, and therefore end up being put in cheaper versions. It's true not only in automotive industry.
Another yes - sometimes same parts are being made with different materials, for various reasons. It may happen that producing higher quality parts is simply cheaper, due to the availability of materials in local market or technological solutions of nearby/cheapest suppliers.
One example mayb. I've made an installation of robotized welding cell in a factory working for a known, old, american company
Parts used came from 2 supplyiers - one asian, other european. Problem with those asian parts was that they rarely passed the entire quality check...Most of them was used anyway, just in slightly modified production process and/or for different end-customer, i.e. other assembly plant.
Sorry, can't give much more details, but the bottomline is - i've seen such practices and frankly I can't say I was much surprised - in the end it's just another way of cutting costs.
EDIT: marcush's post made me realise i haven't clarified, that not passing "entire quality check", never meant those parts were below tolerance specified in desing (I've never seen complete specifications for those parts, so can't tell...). They were just more off the specs than the other, better sort