Comment 7 for bug 1026780

flash-kernel doesn't necessarily know how to change the kernel cmdline. This is extremely platform specific and might often change with user-configured changes. Consider that flash-kernel has to support RedBoot and U-Boot based platforms and that the kernel cmdline args are in the bootloaders' config in flash. The cmdline args might have been changed by the end-user, and it's hard to patch them in place just to set root. The approach of forcing the rootfs in the initrd is at least reliable and consistent across supported platforms.