Are these edits appropriate?
Seems fine to me. Arguably these should have already been linked to Amazon - it's something of a tradition. If someone else wants to pick up the slack, let 'em go for it...
That's not saying the posts are necessarily worth the attention though. However, if you see edits like this made to answers on a lousy question, the first step should be to close the question - then you can reject the edits (or not).
Most of the questions seems to be asking for book titles in the first place. I guess forwarding the asker to the exact book you mean (be it on amazon, Google books or even Good Reads if this is feasible) serves the propose. Books with similar titles are always there, so it saves a lot of time wasted in confusion.
Another thing, I don't think Amazon is in that need for ads, it's the de facto source of books online, + other things :)