The books aren't shrinkwrapped, the slip cased set is. The set needs shrinkwrap to keep the books with the case.
The Core Set is what we were talking about.
If the Core Set is shipped in a nice, tight book box (as would normally be the case), there is nowhere for the books to go until the books are actually removed from the slipcase. The shrinkwrap is superfluous.
And packed en masse, that slipcover is possibly thick enough to affect efficient shipping. 3 Core Sets with slipcovers packed against each other take up the room of 10 books without the slipcover side by side...not to mention the additional vertical space. (The end result would actually depend upon the actual boxes in which WotC shipped its books.)
Again, I can understand if you were making a call to all game companies to be more eco-friendly, but you're not. You're specifically calling out WoTC when they're not really doing anything out of the norm.
I'm calling out WotC in particular because that's whose less-than-friendly packaging I've seen.
In the past 10 years, I've bought lots of game product from a variety of producers- WotC, Paizo, HERO, Heliotrope, Palladium, WizKids, etc.
No other game book purchase has involved shrink wrap. Or slipcovers. No purchase of dice has involved that much extra cardboard, and the plastic boxes they come in get repurposed in game.
In fact, the only game product I've purchased in the past 3 years with significant waste were:
1) CMGs, which by their nature virtually demand non-translucent packaging.
2) Things in blister packs...mostly metal minis. Those I repurpose for working with minis- catching dripping or shavings, propping up things that need to set in a certain position, etc. That said, I don't see how one would change the packaging significantly.
3) The 3.X and 4Ed Core 3 sets.
If you've got something in particular to add to the list, chime in!