Linux kernel it's not something userspace software care about. E.g Linux interfaces that work with userspace are stable so technically you should be able to run really old software on any new kernel if you have all dependencies limit. So main requirement for PA it's version of glibc ABI. As far as I know requirement of PA it's GLIBC_2.14 so any distribution that support this is suitable. For example Debian 7 wheezy only have GLIBC 2.13 so it's unable to run PA without dirty hacks, but Ubuntu 12.04 already have required version.
A lot of projects and software companies list kernel version as a requirement. E.g. http://www.lokigames.com/products/ut/
Got it. In the past new syscalls in kernel appear more often and also it's was big deal to upgrade system. It's no longer true anymore and you can't technically run new game on kernel that too old just because drivers no longer support them.