Wondering about the effect of recording on music-making is interesting enough, but what is a recording? To a listener, anyway.
The recording itself, that physical object (if only patterns on one's hard drive) and one's property rights over it, is a commercial thing, foundation -- in other genres anyway -- of vast fortunes and all sorts of economic activity. But so, in the same way, is a ticket; one would have to go back a long time to find a commerce-free manifestation of art. The content, however, is another thing. Like any night at the Met (or in the dreadful heat of the Great Lawn), one's experience listening to an opera recording is that of a performance, with all the aspects mentioned in the early post here on taxonomy. Let's look at it that way.
(1) Opera on record gives a vastly different sensory experience than its live counterpart. Visuals, obviously. Even the best home imitation -- DVD (or some HD derivative) on a large HD monitor with surround sound -- is far from what one sees from any particular seat of an opera house. There are cuts, close-ups; the action's surrounded by living room decorations; and watching in the dark is rarely practical. With CD one's left with no visual at all; just the living room and perhaps a libretto or score. Or not even these, if one listens over headphones on the street or subway.
But sound, too is different. Even now, with high-end equipment and realistic miking, the recorded sound of a voice is not its live sound. And most producers seem not even to try for realism -- most prominently in Met broadcasts, where a very close miking (at the edge of the stage) inflates vibrato, squashes big voices, and assists little ones. (Not to mention what the dynamic compression of most radio stations does on top of it all.) It seems to me that even sonically, where the things are at their closest, a recording and a live hearing of one night at the opera should be evaluated as two different performances, with what might as well be two different singers (Fleming-disc and Fleming-theater, say).
More about the other aspects of performance, plus general thoughts, in another post.