Well, let me put it this way....
I'm currently working on a thesis for my masters' degree. Is it alright for me to quote a previous work without properly citing it in text, or in my reference page?
If not, what is the difference with not putting the work done by a previous artist on the record?
To use that comparison, is like saying you were cleared for your work being educational. But if you became rich and famous, and your thesis is published, makes you a ton of money ect, and those authors comer back and sue you for not requesting their permission, that is completely fine? Jimmy Page did credit Holmes when they covered the song, but when it was reworked, ASCAP did not recognize the song for being a copy, and awarded Zeppelin a unique license.
If they took the song 100%, word for word, and note for note, I agree, they should have gotten permission and credited the originals. Janis Joplin had such a unique voice, she was never in trouble with getting her own unique licenses for doing the same thing. I swear, many major hits, you'll find this same flaw of influence, and lack of credit or permission.