I think the idea is to bring more than you think you'll need. For example, if I'm heading out on a six mile hike and the temps are going to be around 90, I figure I'll need about three liters of water. In terms of the 10 essentials, maybe I throw in and "extra" half liter or so.
I basically agree with you. I feel that the 10 essentials are really only complete when you supplement them (for me, it's the second set of 10 on my list). Maybe you could remove the bandana from the "essential" category, but it has so many uses including sun protection, (first step) water filtration, bandage, etc.
Yeah, pretty much everyone is on me for that one. Believe it or not I include a lightweight fleece hat (i.e. toque) and gloves in my kit even in the summer in S. Calif. Combine a light weight fleece hat with a trash bag, and you can weather pretty much any summer mountain storm even if you're caught out overnight unexpectedly
I've been around too much and seen too much to not carry what I carry. If you're out much, it's just a matter of time before something unexpected happens, if not to you, then to someone you run across.

Thanks for the comments and insight.

HJ