But you also don't get a guatanteed one boulder per tile dug out (or part-dug out, in ramp.?and stairway? tiles, but it might as well be whole, as destroying such ramps/stairwells never releases a boulder to make up for not having got one the first time round). Only a few things guarantee a dropped item on mining.
You really have to assume that a lot of the digging just produces dust that just disperses (without causing problems with sight-lines, pneumosilicosis, etc). And
maybe that's why a Blue Whale/Dragon/Colossus-sized rock-void gives
merely enough stone to create one earring (or three mugs, or the four aforementioned stone blocks!), and yet that rock boulder (or just one of the four blocks that you get from it!) can perfectly seal off a tile in all six directions (N, S, E, W, U, D), depending on what other barriers it abuts. Obviously the copious yet ephemeral dust is gathered up to seal the gaps, during construction.
For floors, however, note that Bridges and Paved Roads need less units of the material to cover the same area. (Bridge construction doesn't let you hang things off them that aren't already able to hanging off other infinite-strength anchoring structures/topology, and road construction requires an already solid and flat(ish) surface to lay upon and can't act like bridges in their own right... Maybe because they're lined with even
more dust, to make up the material requirements, compared with constructed floors.)
Just some of the screwy 'physics' and 'civil engineering' aspects in DF. Best to just roll with it, until and unless Toady decides to annoy a lot of us old hands by rejiggering it towards 'realism' and causing us the same kind of pain as he changed it from novice miners mostly just emptying spaces (when we actually might have wanted initial building materials) and legendary ones mostly producing stone lumps (when we were probably more interested in clearing out spaces) and forced us all to readjust our copying strategies (train some miners up on no-drop soil-digging, then use newbies to clear areas and the trained ones to get the stuff we
wanted).
Or something like that. Something always seems to change, and I'm not entirely sure I remember
exactly how it has changed over the last decade or so...
E&OE