An acquaintance built an entire home completely by himself, including an all-wood foundation (though, sitting on a concrete footer). It certainly was simpler and quicker to build. Material-wise, I don't think it's cheaper - the cost savings comes from the savings in labor. Unless I'm mistaken, it calls for marine grade plywood, not just ordinary pressure treated plywood. If I did it, I'd want the plywood also made of larch, which alone has some excellent ground moisture contact properties. But, marine grade plywood runs around $80-$100 per sheet for 3/4" to 1". That's 32 square feet for $100, not including the studs to support it. By comparison, it would take roughly 2-3 dozen masonry blocks to cover the same area. If you used 16"x12", it would take 24 blocks, which at HD's prices (quickest reference), are just a little over $2 each, or $56.68 for 24 at the current price. (It would cover slightly more than 32 square feet, since there's mortar between blocks; mortar is pretty cheap too. Rebar for the block/studs for the plywood, and material wise, those come close to evening out. I'm not sure what the expense is of spraying the outside with a heavy duty water proofer is, but it should be done to both.
I would NOT buy a house that had been built by a contractor with an all wood foundation, unless I was absolutely certain they used a high quality marine grade plywood. Too many builders seem to cut corners to make more of a profit. Regular pressure treated plywood simply doesn't last long enough in contact with the ground.