They all offered a VPS, which is basically a Linux box with root access. Any Linux tutorial would work on all three services. I'm not arguing if DO was a clone

They all offered a VPS, which is basically a Linux box with root access. Any Linux tutorial would work on all three services. I'm not arguing if DO was a clone or not, but saying that "you could use Linode/Slicehost documentation because DO was a clone" is a bit of a stretch.