I think I agree and disagree with what you say.
In the "traditional Unix" department, I'm strongest with AIX. It's IBM's flavor,a dn it only runs on their hardware. They do a LOT to make the HW and SW work hand in hand. They have a lot of options to prevent problems or reduce them to non-disruptive (for the end user). They have a lot of admin options that don't require reboots. For virtualized systems the default setup had "dual VIOS" (Virtual I/O Servers) so you can muck with them including rebooting while keeping your virtual machines ("LPARS") purring and happy. If you need big boxes, especially if you are scaling UP instead of OUT, they'll give you a level of uptime that's better than linux can. Becuae (a) less administrative disruptions, (b) less unplanned outages causing disruptions, and (c) only runs on dedicated hardware so it's avoiding all the extra issues that come with that.
However, if you're got an application that scales OUT, Linux can give you better total uptime simply because between hardware and OS licensing you can afford to have more of them. If I'm looking at 50 IBM POWER systems running AIX, vs. 120 linux blades or pizza boxes, and taking any one of them out still leaves your apps available with just a little hiccup to the users who were on that host, that's hard to beat.
These examples both assume that you know what you're doing. Anyone can muck up a machine, being more expensive doesn't protect against that.