Every Gentoo and Arch install is a special snowflake, with whatever the latest stable versions were when a package was last updated. Rolling releases are awesome -- the software doesn't have to ship in a goddamn box!
RHEL + Debian are constantly backporting and patching so much crap onto their 'frozen' versions of upstream software. For them 'stable' means that you get the pain of updates without any visible features, with the added annoyance of hacked-in patches from people who didn't write the software.
For this reason there's pretty much zero pain to Debian Stable updates. I cannot even think of a single instance off the top of my head where applying buxfixes on a Debian Stable box has caused any problems at all.
Well, a certain commented-out line in OpenSSL comes to mind :-)
But seriously, I refuse to run anything other than Debian Stable, Ubuntu LTS, or a stable BSD tree on my home systems. I rely on my desktop more than I rely on any given server, so why would I put something less stable on it?
Sure, we probably all stare at our desktop machines for hours a day, and only poke at our servers for a few minutes each day. But, an hour-long outage of my primary server will effect hundreds or thousands of people. An hour-long outage of my desktop will effect only one guy. I'll spit and sputter and curse a lot, but it probably won't cost me business or customer good will.
That said, everytime something breaks on my desktop machine running Fedora, I think "Hmmm...maybe I should be running CentOS here."
I used to run arch. Forget to update for a few weeks, and you could almost guarantee a broken system when you tried. It was even worse with Gentoo.
Say no more. I didn't know Arch was the bastard child of the abomination that is Gentoo. Best of luck with that.
Arch also compiles it's packages for i686, to appease the gentoo-ricers.
Their goals are similar, so you could argue that Gentoo inspired arch, but they are unrelated.
The only reason people keep mentioning Gentoo around Arch is because Arch is occasionally concerned with speed and they're both seen as nerd distros.
rolling release does not mean you have to upgrade to python 3 if you still want to use python 2.6. it is very trivial to configure pacman to ignore certain packages.
Stability and predictability is vastly more important than having the most new-fangled of everything. Fedora or Ubuntu (non-LTS releases) are nice desktop systems, and they have all the latest fancypants stuff built right in, but I'd laugh someone out of the room if they suggested running them on a server. Arch doesn't even appear to have an official policy on lifecycle, so it's definitely not in the running.