This is even more extreme with Grey Knights - even though much less people play those, the number of minis surely outnumbers the "real" Grey Knights by orders of magnitude. Heck, just a single Grey Knight army organization plan - 3 Elites, 6 Troops, 3 Fast Attack, 3 Heavy Support, an army that could be owned and played by a single player, can theoretically field just about half of all the psycannons that officially exist in the WH40k universe, and have more Purifiers than exist in the entire chapter most of the time!
That is a fact that never fails to amuse me. I actually feel terrible sometimes when playing DoW I or II. Dreadnought down? Why, build another. Or two! Those got shot down? We have reserves!
I mean, I bet it is rare for Space Marines to die during an engagement, especially with an inferior foe, but in the game, they die in the masses.