first of all, there are supposedly a bunch of different units , all pre production, with different releases of the firmware and probably slightly different hardware inside.
secondly, the other member on this forum having a touchstone 2, commented on that review ( check the various comments)... according to him, his unit has
1) very good audio output
2) a different finishing on the top , that prevents scratches
even the fact that these docs do not have the "glue material" on the bottom is relative, since they are test units. There is nothing that would have prevented the final release product to have such thing added, in their plans, nor to have more weight added to the whole frame , or to the base.
But for a test item, why should they have spent more for weight or glue ?