In Linux API stability is generally provided by the rule that if you change the API you have to fix all of the drivers. If there are a lot of drivers that is a lot of work to change everything.
So if an API changes under you (in linux) for a driver that means either you are using something esoteric that few other drivers use and their was very little pain in changing it. Or you are using something for which someone felt the pain of changing it was worth the gain.
Since it is a lot of work to change an API with a lot of users the churn rate should be reasonable, and it should not need to be a full time job.
Where have you seen the rate of change in the linux kernel APIs churn so fast it was a full time job to keep up?
And yes there are periodic rants about not changing the driver APIs too much as well.