backpacker :
I said making firewood, not kindling or fuzzy stick.
Part of gathering fire wood is making the fire, it takes quite awhile to build a fire to the stage it can handle 10" wood, even if well seasoned. This is also a rather extreme case of fire building, even 2-4" diameter wood will last several hours unless it is clear pine which is horrible wood to burn as it gives no heat and is consumed at a rapid pace.
As well unless the weather in the area has been very fine for quite some time, even dead wood is far from dry, and if all the wood is very dry, fire building is trivial in any case. Try making the fire after heavy rains and see how useful a piece of wood over a couple of inches becomes, not to mention the shear weight of just moving it.
You also specifically mentioned shelter building, and for many of the associated tasks a long blade is many times more efficient than a saw (shelter should also encompass clothing and assorted tools). If you had limited your statement to "A saw is more efficient at bucking thick wood than a axe or long blade ..." then there would be little disagreement, as this is why saws replaced axes for loggers. There is however a lot more to wood work than just bucking thick wood.
For general outdoor working it is unnecessary to cut through 10" wood for building a shelter or making a fire, and it is dangerous and extremely wasteful of energy considering the effort it takes to fell, move and buck that size of wood even if you are working on a dead and windblown tree especially if it is in any way humid or sees even infrequent rain.
... a knife will not cut hard dry wood very well.
A poor knife won't, but a crappy saw won't either. Yes if you take an excellent saw and compare it to a heavy tactical thick ground knife the saw looks wonderful for almost any wood working, this has nothing to do with blade vs saw, try a long blade with a profile similar to the Valiant Goloks.
The saw, knife and Leukku weigh less than a big knife and are more versatile than a single tool. I don't know why I would carry a single tool.
A long blade still has advantages in gathering light vegetation over all three of the above, how significant this is depends on the enviroment, it can be critical in some, of no consequence in others. It also can work better for various wood shaping activities such as work as a drawknife. But yes in general you are more prepared the more gear you carry, I typically take a small folding saw, small fixed blade (3-4") and long blade (~14" similar in nature to a Valiant Golok).
The long blade handles any brush work and felling assisted with undercuts from the saw if necessary which is rare (ring knots). The saw does any bucking on difficult to cut wood (really knotty) and the blade splitting assisted with a mallet. Felling and bucking and splitting are rarely necessary though as you can usually find enough firewood just by using the dead trees, and clearing some of the dead branches which can be done easily with a walking stick. The small blade handles any light cutting which is just too awkward for the long blade.
One shorter but still of decent length blade can handle all of those tasks (though none as well) you give up machete type use to get some mobility for precision cutting, this is the common 10" bowie pattern. The main advantage would be in simplicity, having to care and maintain just one tool, and it is generally more robust, plus you could probably afford a better quality one, having only to buy the one tool[*]. But you always have to make such gear compromises. For example if you packed two saws you would be more prepared than just one. One dedicated to hard woods and the other soft, very different teeth patterns and even steel composition.
In the winter I would tend to carry a small axe rather than a long blade because then there is no use of being able to cut light vegetation as all of it is hidden under feet of snow, and the wood is much harder and stiffer and the axe then is more functional for felling and works better cutting holes in ice. The long blade can also be switched from a long slender golok or Kobra type pattern to a heavier Ang Khola khukuri pattern to achieve much the same goals.
[*]In general this isn't true though as you can buy top quality folding saws and small knives very cheap, a quality longer blade, even of the same quality will be more expensive than those combined, though you can get solid blades that are not terribly more expensive, the HI khukuris, and the Becker and Swamp Rat knives.
-Cliff
