[johnkeegan]

I've noticed a misnomer that keeps getting repeated here. If mulch is not in contact with soil (because of weedmat) it does not turn into "soil" unless soil is added to it. Mulch is straight organic matter. Soil is "10-20% organic matter (decayed plant life, such as mulch), 80-90% mineral matter (rocks, sand, silt, clay)," as quoted from the "Victory Garden Landscape Guide," Thomas Wirth. (The only handy book I had with a "soil" definition).
Now if soil gets mixied in with the mulch from planting, bed edgings etc. I guess it then can be classified as soil.
This is why (near) 100% organic matter such as "mulch" is effective at retarding most (not all) weed growth and germination. Leave a pile of straight mulch and a separate pile of true soil in an open area and see which grows weeds first.
But once you allow the mulch to come in contact with the existing soil you create a richer soil than you originally had, which the weeds love once they can sink their roots into it. The landscape fabric creates a barrier between the true soil and the organic matter (mulch). Thus not only slowing the decomposition of the mulch but also preventing the creation of that super rich layer of soil under the mulch, which is like a shot of steroids for the weeds..... And, no it's not good for the plants you installed to have that super rich soil at the top. Encouraging roots to grow up is not a good idea long term.
...sorry for the boring soil structure ramblings.
..and Tricky,you say, "it just kind of leaves a bad taste in my mouth to install something so permanant and unnatural," I don't about you but I install alot of pavers and segmented retaining walls (with geogrid). They're quite "unnatural" and I hope they're around for a long time but it reallys doesn't create a moral dilemma. And which is more damaging to the environment, landscape fabric or weedkiller, which you may not personally use but along with pre-emergents seems to be the preferred way to combat weeds.