Can we quit the OS-wars finger pointing, please? Prior releases of MVS, VSE, VM, and so on did require a reboot to change the clock. They also tended to use local time on the HW clock. (We do now all use UTC on the HW clock, don't we??) (Rhetorical question there, folks.) But that was then.
So now, z/VM might be hosting an old guest, one that requires a re-IPL to change its time zone. VM cannot magically make things right for such a guest. But for those which (like Linux, or like contemporary z/OS or VM-on-VM) can handle time zone changes without a reset, there is no more need to reboot either them nor VM. What Alan said: Linux, like all UNIX (that I know of) uses GMT internally. "Time zone" is an application concept. Any single app (or any given user) can run in a different time zone. VM effects this with TOD offsets for any guest. I think that, sadly, too few of us utilize this. But we should! Stop rebooting your VM systems needlessly. Vive le hypervisor! Abat le reIPL!
