You have to do that because Oracle has a nasty habit of changing what’s in the download and then changing the licensing scheme.
I’ve been burned by this before, and gone as far as to require a 3rd party audit for Oracle installations on a quarterly basis.
Are you referring to updating one node at a time of a RAC cluster or is that some other method?
Yes that is what I'm referring to. But note Oracle has the concept of a single node cluster, so you can have a completely standalone deployment and still perform this technique hot adding a new "node" when it's the same server.
Of course, you've still got to obtain a patch. I usually see the licensing in the name of some senior manager who doesn't know how to use a keyboard and who is also the only person allowed to download patches.