I don't actually agree with that - it's still pretty processed and brickwalled. Compare it to, say, some of Toy's old albums (I mean that stuff was layered exquisitely, beautiful if you have the CD version - my personal test track for ambience), or a lot of the old pop really.
But why? Well you could say that too much of a good thing makes for a not-so-good result.
When you produce every single smidgeon it sounds awfully processed. They can throw all the producers they want on it, it still might turn out to be an overproduced mess.
Heck some of my cassettes from back then sound a tad better than what they're pulling out, in terms of dynamics. Grainy mess though.
Did you try the H.O.T. track? The CD version is beautifully dark, hits like a boss, a lot more vibrant than say, the distorted bass blobs and flatness from most other SM stuff nowadays. Whoever did BoA's new CD did okay, but still could have done better. Loud and lack of grain should not necessarily be considered better with regards to recordings.
And of course with regards to the truly awfully-mixed old pop - well that grain makes for a pleasurable nostalgic vintage feel, no? I love that feel - it's why a good portion of my active home listening's still on cassette + a old stereo.
Not that this has any impact on whether or not the music is damned good or not (I could care less how it's mixed - really).