/linuxrc is launched on an old-style initrd,
/sbin/init is launched on a newer-style initrd,
/init is launched on an initramfs. Initrd and initramfs are two mechanisms with the same purpose: to mount a filesystem in RAM from which storage drivers can be loaded. Initrd is older, initramfs is the current recommended method.
Some distributions have kept a setup from the days before initramfs existed, and call the image initrd even when it's an initramfs image. So the fact that you have a file called
initrd does not mean that it's loaded as one. Some distributions, evidently including yours, have kept a file structure on the initrd/initramfs that allows the same directory tree to be used on either. The format of the image file is different, however.
To figure out whether you have an initrd or initramfs, the easiest way is to run
If you have a cpio archive, it's an initramfs. If you have an initrd, it's <rummage> “Linux Compressed ROM File System data”.