What we're really talking about is mastering for different formats, not mixing. And it makes perfect sense. When mastering the audio for vinyl, you need to carefully control the bass or the tone arm will fly. When mastering for CD, you're trying to manage the dithering and samplerate conversion, etc.

Make perfect sense to me that someone would master differently for an MP3. And there's no risk as technology changes. Mix to get a good balanced sound, then master as appropriate. If the technology changes and you need to revisit things, remaster it again.

jw