Both. Good support is expensive and rarely a "just". Adding a new supported platform means having to train your support techs in all the quirks that come out in

Both. Good support is expensive and rarely a "just". Adding a new supported platform means having to train your support techs in all the quirks that come out in using said platform, and those little things add up in a hurry. On the technical side, each distro has their own similar, but not quite the same, different set of patches against base software and build options which can potentially interact with your software, etc, all of which will need to have regression testing done against before release. Furthermore, software like RHEL itself is supported for a known duration of time, so developers can build their own release and support schedules and not have to worry about getting the rug pulled under them.