This appears to me to be an outgrowth of link-only answers, except worse in a way (because while links are often possible to visit without paying, many books/movies/etc. require you to pay for them). Even interlibrary loans of the works in question may not be available everywhere.
However, an answer that basically states "you can do this in manner X by A, B, C, as for example Delta Echoson did in Flurry of Grimmicks" is very different from "Delta Echoson did this in Flurry of Grimmicks". The former actually answers the question (and can be judged on how well it does) and provides a reference for those who wish to find out more, but the reference is not required to understand the answer. The latter makes the reference absolutely essential to even understanding the answer, and without access to that reference, the answer is meaningless. Ideally, of course, an answer that provides references of this kind would provide multiple references by different authors.
Do consider Your answer is in another castle: when is an answer not an answer?. Based on the same line of reasoning:
- answers that simply state "read this book" should be either improved (by incorporating relevant details into the answer) right away, or flagged as "not an answer" and either improved through the review process or deleted, the same as you might a link-only answer on most other sites in the network
- answers that state "read this book where it's done like this" for some low value of "like this" should be encouraged to improve upon, but they are answers because when you strip away "read this book" it still provides useful information to the person asking or later reading the question
- answers that state "you can do it this well-explained way, like for example this author does in this book" are good because it answers the question and provides references for those who want to learn more about how others have used the particular element they are interested in.
All of this assuming, of course, that the answers really do address the OP's question in the first place. If it doesn't, then it should likely be edited, or downvoted and/or commented on to have the answer improved.
The above-linked MSE question says "strip the markup" (including links). Here, we might say "strip the references". Does the answer still make sense, and does it still answer the question? If it does, then it's probably an answer; it might be a good answer or a bad answer, and it might be a correct answer or a wrong answer, but it's still an answer. If the answer does not make sense without the reference and/or markup, then it should probably be flagged as "not an answer" and treated as such in the review queues.