Usually system manufacturer's fault. A recent example where I work is Lenovo's recommended Intel wireless driver (the one on the Lenovo site) was over six months old and had known issues with causing machines to not be able to wake from suspend. Installing the drivers directly from Intel resolved the problem.
That's pretty much the best case scenario. A lot of chipmakers (Conexant, Jmicron, Intel in many cases) don't allow you to download drivers directly from them. So you are stuck with whatever the OEM provides. In some cases I've found that newer model laptops by the same OEM use the same audio/media controllers under the hood in some case and I can use the newer driver from the updated model.