Earlier quoted context omitted.
For the majority of people, mp3s seem to be "just as good" enough. I remember some low-bitrate songs encoded with some very early encoder where you could hear a difference. Not necessarily "the" difference but "a" difference. After a couple of years the worst encoder anyone could find was better already and since 192kbps bitrates mp3s were 99.999% there. I'm sure that a trained ear can hear differences between 256kbp…
The conventional wisdom is just that - MP3s don't sound any different than their CD counterpart, but we all know that they don't have the same degree of fidelity to the original mastered audio files. While it is true that most cannot detect the differences between MP3 (and other lossy formats) and PCM (lossless) audio, this is beginning to change as consumers become used to a higher quality of sound delivery than bef…
The only way any consumer will ever notice that music is from an MP3 is if it's a bad encoding. That's the fault of whoever chose the encoding parameters, or picked an obsolete encoder. But even CDs aren't immune from stupid people. Lots of poor quality CDs are produced. I actually bought a major label CD with a song that clipped! It was mastered so loud that it clipped, and they didn't even bother to fix it. That's the sort of problem you can detect with software -- if you're deaf, because even my grandma could hear the flaw. How that got released, I'll never know. Yuck!
Only music producers may notice the "decay" you speak of. MP3 compression throws away data. It's data that no human ear can possibly hear, but when you're in the business of making music, you want to do things like process samples to change how they sound. It's possible to transform uncompressed audio data to bring out sounds that weren't audible before. Those inaudible sounds are likely to be thrown away by an mp3 encoder, making that sort of processing impossible.
But even CD quality PCM audio isn't lossless. It's perfect for listening to, but it's not great for processing. Music is often recorded and processed at higher bit-depths and frequencies before being compressed down to CD quality. You can't possibly hear the difference among studio quality 24 bit 192 khz, CD-quality 16 bit 44 khz, and a good mp3 encoding -- but the studio quality data gives you more processing headroom.
The photography world has analogous issues. Professional photographers and serious amateurs often shoot "raw". Their camperas are capable of producing normal jpeg files, but they don't use that feature. Instead they shoot and process massive, uncompressed files containing the raw sensor data. They then export the processed raw files to jpeg for publishing or printing. You can't see the difference between a raw file and a jpeg. (Actually, a jpeg straight off the camera often looks better than the raw file because the camera does a bit of processing.) The reason photographers bother with the big, unwieldy raw files is that they have more processing headroom. If a raw photo is too dark and there's a big black shadow in one corner, you can ofter brighten it up in postpressing and reveal the flowers that were there. If you do the same to a jpeg, which has much less information, the big black shadow will often brighten up into a big gray shadow. The "invisible" detail in the flowers has been thrown away during compression. The point is, the original unprocessed images looked the same. The differences are invisible in the same way that the differences between CD audio and good mp3s are inaudible. The differences only matter when you go to process the data.