[red-iron-pine]

Bingo.

There is no AIX or HP-UX in the wild anymore, at least not outside of niche or legacy deployments, because RHEL ate it up.

Every enterprise I've ever been at required official licenses and official escalation and support SLAs. By offering enterprise support and reasonable response times they became the de facto winner of the Unix enterprise world.

Ubuntu still reigns supreme for individual users, but they're a drop in the bucket compared to F500 companies.