@Ram
That's the kind of conversation an engineer would need to have after listening to the stereo mix premaster, so yup they are doing things correctly
There are a few companies now which accept the bounce down files for individual instruments or grouped instruments. I.e. A bounce of drums, a bounce of guitars, vocals, etc. You mix them see when stacked they provide the full mix as you want it, allowing the tiniest of tweaks for headroom. It isn't remixing per se as when changes are made they are done as non-intrusively as possible, and often to compensate for changes in the feel of the mix/relative levels made by mastering compressors/EQ to
get back to the mix you started with! Mastering is still mixing; compressors, limiters, EQ... it all colours the sound!
I view mastering differently to dedicated mastering engineers I guess. For me, mastering from someone else's stereo mix will very often involve compromise. Mastering is an extension of the mixing project for me due to the way I work. I am aware of this but I would never be a dedicated masterer... it's not the right job for me
My own point I want to mention here:
Just because products are mastered by big studios on big labels does not mean they are done well. In the late 90's there was a run of albums that were squared off. Ruined. "Californication" by Red hot Chill Peppers and a couple of Oasis albums were victim to this. Certain tracks off those albums are unlistenable to me, especially on headphones. Guitar clipping is very apparent, vocals too in places.
http://en.wikipedia.org/wiki/Loudness_warIt has become less of a problem in the new century. But I am finding that masters are still too heavy on some CDs; vocals too flat dynamically, drums lifeless and one level. All just to sound "louder". I find it sad. We have volume control! And radio stations compress anyway!!
For a great example of modern mastering go listen to your Laura Marling albums; the second and third album manage a great balance of modern with dynamics