contrary to what other people think, when you retrieve the insertion point of a block , it WILL give you the exact coordinate. You may not "see" it, but i tell you now. IT IS.
Try inserting a block at 0,0 coordinates. and move that block 0.0000001 then use
You will get something like (1.0e-007 0.0 0.0)Code:(Cdr (assoc 10 (entget (Car (entsel)))))