I believe it's difficult for ARM to merge driver fixes into customer branch, due various reasons and one of those is a possible customer concerns about regressions and the need to revalidate all of their test content. How many opportunities to include fixes do you have (if there's an average number). Is it mainly when OEM ships new product or it could be considered as part of a major os update?
It's entirely down to the device manufacturer what patches they are willing to take, and the update schedule for their devices.
Regards,Pete