Some people are still on 56K, you know. Back when I had dial-up, any file more than 5MB in size was out of my reach, since my internet connection would drop long before I ever finished it. Download managers like Getright could help some, but with dynamic hosting that's so popular these days (The direct URL link is never given to the user and changes constantly), even those are useless. The only real way to get anything done was to use Torrents, and those made my internet slow down to the point of being unusable for several days at a time, and all that time I had to sit there, reconnecting if it disconnected (since the auto-redial usually failed). It's like getting a root canal in your balls. If every quest had a bunch of MP3s integrated, I'd probably have killed myself.
Although I would LOVE to have a way to do more with MP3s, like have selective loop times like with MIDIs (Since a lot of MP3 tracks that would be great for game music have an intro/outtro, which makes them terrible for direct looping), being able to integrate them with Quests would be a horrid idea. And you honestly think people will only include a couple of minute-long MP3s? Honestly, give me selective loop times and my quest files would easily go over a gig.
As for QSMs, love the idea, now just add looping :3