A few comments:
Bladder Sleeve: I never use a bladder connected to a tube. However, when I carry water, I always put my platypus in there and think it is a good idea. I've never crushed the water bottle, nor have I ever heard of anyone crushing their water bottle in that manner. On the other hand, I've heard of folks losing their water bottle, when it is on the outside of the pack. You also ignore one of the main benefits of having the water sitting there. If your water container is full, it is likely the heaviest item you are carrying, as well as the most dense*. For that reason, it makes sense to carry it very close to the back (to reduce torque).
* I'm not sure how the density of water compares to the density of other items (that's your job and you folks at BPL usually do it really well).
Zippers vs. Drawstrings: By and large, zippers are heavy. A small zipper to hold a wallet may not weigh much, but a heavy zipper securing a compartment will weigh more than a drawstring. Zippers are also limiting. You can over stuff a compartment and still secure everything when you have a drawstring opening -- not so with a zipper.
Extra Compartments: Like extra zippers, extra compartments add weight.
Pack Bag Weight: This is why it is difficult to just compare the weight of a backpack, the way you would a different piece of gear (like a tent). If one backpack weight two pounds because it has a very firm hip belt and shoulder strap, along with a solid frame, then the extra weight may be worth it. One the other hand, if a pack is flimsy, but has lots of straps, zippers and extra compartments, then you're just carrying extra weight. It may be more convenient, but ultralight backpacking is (to me anyway) about doing without some conveniences to save weight. Judging the efficiency of the pack bag itself would lead to a much better comparison. I would love it if pack makers listed the weight of just the pack bag. That way, you could easily see whether an extra zipper, compartment, or even a bladder sleeve, is worth it.