You know the sound of a record after it's been abused or simply played too many times? You have pops, cracks, and hiss that are a fundamental problem to the listening experience? Imagine if a band let a new CD go through with that kind of stuff on it and you would have an idea of what it's like for those of us with decent equipment and discerning ears to try and listen to this poor mastering. Yes, I can hear the music and enjoy it, but there is no reason for it to sound like it does. It could be the band wanting it to sound that way, it could be the band sitting down with an engineer who really doesn't master any other way, or it could be them being completely hands off in the process, but in any case it's still a poor mastering job.
While the focus obviously has to be song, things like the cover art, sound, and overall presentation all go into the business of a band, and while I still considering Dream Theater to be masters of their craft where it counts most, it is saddening to see them somewhat waiver in these other aspects.