Warning: speculation ahead.
I think that those lifespans are more likely to be a "minimum aimed lifetime" rather than something else.
What leads me to think that is that lab testing is costly, and some tests are also verytime consuming. Take stress-testing (testing for material fatigue) for exmple. Flexing a component repeatedly until it fails. My guess is that those tests must be performed on a statistically significative sample. You either build several machines to test several prototypes at once or do it one by one. Im also assuming that testing for 2000 km needs the double as to test for 1000 km.
Taking that into account, there must be a certain point of equilibrium between how much to test something, and how sure to be of the spected lifetime of a design, o a production batch. This is much more important in low to mid priced items, because they are sold in higher volumes, so a tiny cost saving gets multiplied by huge quantities.
Higher priced items on the other hand tend to be more exclusive, much less units are sold, but also, all that testing is even part of the marketing of the product, and the target market is likely to "appreciate" all that testing and quiality guarantees, i.e. it's more sensible to test these products toward higher extents.
That being said, I doubt that there is something "conspiracy theory" styled argument towards purposefully designing a mid-range or low-range component to fail after a defined time/usage span. That would add up to the design and development stages.