I think that "stack & whack" and "1 block wonder" are brand names for different patterns/designs. Both are made similarly - by layering fabric repeats on top of each other and cutting out identical pieces to use in a block to create a kaleidoscope effect. I want to say that "stack & whack" is older than "1 block wonder", but that could just be the order I first heard them. I've seen these quilts done with as few as 4 pieces in the block and even more than 8.
Pulling out my "Magic Stack-n-Whack Quilts" book. It covers a variety of blocks - Half-Square Triangles, 45 degree Triangles, 45 degree diamonds, 60 degree triangles, 60 degree diamonds. Looking at the pictures, the quilts call for the main fabric and a background fabric.
Remember the 1-block wonder's I've seen, I think the quilt just uses one block (the hexagon or the 60 degree diamonds to make a hexagon) and only uses the main fabric.
I could be wrong in my classification of the two, but from what I've seen, this is what I've observed.