Hide Forgot
When trying to create a partition for /boot on an LV, anaconda tells me "Should be on a bootable partition". GRUB2 (and possibly others), ARE able to boot from an LV. Thus, Anaconda should not block /boot to be on a LV, as there's no guarantee that the bootloader used will be the GRUB Legacy, distributed with the installer (e.g. when dual-booting with a different Linux distro). Anaconda is ofcourse entitled to give a big warning on this, but should not block the install. On a more personal note: This is the only thing from keeping me from just PV'ing /dev/sda :)
grub is the official bootloader for RHEL6, so that's what we have to program for. We must block because the bootloader we use does not support /boot on LVM (at least not on x86) and we can have no guarantees as to what you may be setting up later. This situation may be resolved for RHEL7, though.