Sadly, while I totally agree with Zoneman's answer, and it makes sense on paper... really, BioWare? It's a weapon of massive destruction, I don't really think it cares that you've got more foot crunchies or not. I don't remember the Enola Gay minding how many men were on Iwo Jima when it flew to Japan. Just saying...
The over 'Effective Military Strength' and 'Galactic Battle Readiness' is really more of a way for the player to gauge how well they are doing. Honestly, trying to change the 50% Battle Readiness only changes a few lines in the game, and has no other significant impact (and if you didn't know how to change that, play the multiplayer on-line). I'm not sure how much you need for the Combat/Support strength ratings to get the endings you want, but you can skip out on a few easily without any real detriment. All those people worth 25 or 30 points (like, um, scientists, former allies, and seriously the Destiny Ascension, touted to be the most powerful of the Dreadnaughts, and is just as effective as Jacob Taylor?). Some decisions and efforts don't go to waste; the Leviathan Corp is worth 400, and most of Hackett's Dirty Laundry Runs usually gain you about 100-150 for your troubles. You honestly get decent points on recruitments; telling the little arguing folks to support the war effort, or join to go shoot somebody, more so than planet-scanning in some cases.
It makes no logical sense that a deathray machine that would make Darth Vader proud would give you such different results over minor changes. It would make more sense that say snagging certain allies and scientists would change the outcome. Having Rachni drones on the Crucible makes much more sense for a more positive outcome as oppose to... Strike Team Theta. I liked the Quarian/Geth issue; choose one or the other, and choices made in a previous game gave you the best of both worlds option. I wish that BioWare had done that more. Killing off the Counsel in the first game gave the Turians more ships supposedly, but you wouldn't notice it. Too many decisions and choices didn't seem to have affect whatsoever, or just a little bump on your galactic readiness. Concept was great, but delivery not so much.