Having gone through Graduate School and made extensive use of the Engineering Library, I wouldn't say that.
There are plenty of librarians that shelve the books, etc. These are the people that you are thinking of. It is necessary, but as you described, appropriate for a lower paid position.
The ones I am thinking of are the "Librarians", the real ones. These are the people that understand what is in the stacks, make recommendations on new acquisitions, set library 'strategy' and budgets, and consult with Professors and patrons to determine what is needed. Walk in to one of these places with a question on any obscure topic, and they can tell you the top five books in the fields, whether they have it, and if they don't who does, all from memory.
I mean the people who know what the cutting edge researchers in a field need before the researchers themselves know it.
But I still stick to my premise: their median wage shouldn't logically be higher, than machinists.
Now, if we were talking authors -the creators of ideas - that would be a different story.