Don't discount the people doing the offense too much. At some points during the first world war, using well placed artillary, the allies could mount offensives with even or even less casualties than the germans. (and then take much more casualties then the germans while defending what they'd just captured. The problem with defense is that your sitting there, forced to do it, while the army on the offense can choose the time and location of its attacks. Again, its all about, not just hte people in the highest level of command, but all people in command. Initaive is very handly on the battle field. The well planned and precise artillary barrages in WW1 were great when they worked, however when something wen't slightly slow or fast, say, the barrage finished 5 minutes early, yet the offices on the ground (we're talking captains, majors, not the genearls planning it), don't have the permission or initiative to get the offense moving then, and instead have to wait the 5 minutes after the barrage has stopped while the enemy gets ready, then you have problems, and the bloodbathes of WW1 trench warefare.
As far as army size goes, a lot of countries are high on the list due to mandatory conscription and reserve duty. During a time of war, very large proportions of able bodied males would be called up to activly serve in the miltary (eg, countries like tiwan and south korea)