I believe you are all missing a factor when considering a tapered screw. Wood does not act as a solid as metal does. If a straight screw is used, only the threads have purchase and the wood can easily shear. A tapered screw will wedge its way into the wood and the wood will have a vise like clamping affect on the screw. This may double the holding ability of the screw. Longevity is dependent on the number of cycles in/out and the density of the wood itself.
This wedging has to be considered in light of whether or not a pilot hole is drilled for the screw, the size of the pilot hole, and whether or not it is a straight sided hole, or tapered like the screw shank, and the type wood being used. I have a set of tapered pilot hole wood bits. If sized properly for a piece of dense, dry wood, like gunstock walnut, not much wedging should take place, due to a danger of splitting. Same with heart yellow pine and some others. It is all about the application. There is a paper available to read that was published by the U. S. Bureau of Standards about 1926, I believe, which demonstrates the holding power of various wood screws in various woods. Interesting reading.
SRH
