>"I understand your point, but what good are master tapes if they're not available to be heard?"

Because they are they are the source for the products that music fans by. Remixes, re-issues, box sets and alternate takes all come from master tapes. Without the masters none of these things are possible. You are in fact "hearing" those master tapes just a copy of them. It's an incredibly privileged few who are able to sit and listen to the original 24 track 2 inch reels in a recording studio. VH1's show "Classic Albums" show often does with the artist and producer/engineer as the format of their TV show. It's worth watching for this aspect alone. There is a great example of why this is important in the article regarding the 50th Anniversary release of The Beatles's Sargent Peppers. These things would not be possible without the master tapes. The first generation of CDs in the 1980s are laughably bad fidelity. Now imagine the masters for many recording disappeared after those horrible fist early 1980s releases. Those terrible CD versions would be our source of everything going forward.