The difference between initrd and initramfs?

I think you are right in all.

The difference is easy to see if you follow the steps needed when booting:

initrd

• A ramdev block device is created. It is a ram-based block device, that is a simulated hard disk that uses memory instead of physical disks.
• The initrd file is read and unzipped into the device, as if you did zcat initrd | dd of=/dev/ram0 or something similar.
• The initrd contains an image of a filesystem, so now you can mount the filesystem as usual: mount /dev/ram0 /root. Naturally, filesystems need a driver, so if you use ext2, the ext2 driver has to be compiled in-kernel.
• Done!

initramfs

• A tmpfs is mounted: mount -t tmpfs nodev /root. The tmpfs doesn’t need a driver, it is always on-kernel. No device needed, no additional drivers.
• The initramfs is uncompressed directly into this new filesystem: zcat initramfs | cpio -i, or similar.
• Done!

And yes, it is still called initrd in many places although it is a initramfs, particularly in boot loaders, as for them it is just a BLOB. The difference is made by the OS when it boots.