You're right about DBT being very difficult. I'm a believer in DBT, provided the associated gear is good enough. But I will also concede that occasionally something you can't immediately ID in an ABX comparator-type test can still lead to fatigue over time. I don't have a good explanation for it, but I've just experienced it too often myself.
While it's not super scientific, I have conducted my own tests using some willing guinea pigs. I've synched identical CD players up, one with a compressed disc and the other an identical compact disc (same track sequence & level matched as closely as I could) with various bitrates. Even at 256 kbps the subjects in my little test didn't have a lot of trouble hearing the diff.
Of course, that's really only an indictment of Nero & MusicMatch Jukebox encoding in conjunction with the gear I was using. There may be a lot better encoders- if you know of them, I certainly wouldn't contradict you. MP3 may have a bit of an undeserved bad rep, but in my experiences with it, I've never heard anything that approached "hi fi."
But I also think, after listening to a lot of DVD-A (and to a lesser degree, SACD) that Redbook itself is only marginal. Even the best MP3 is only going to approximate Redbook, which is noticably inferior to good 24/96.
Comparing MP3 to DVD-A is like comparing a covered wagon to an F-14, IMOHO.