This comes nowhere near the issue. A soldier's score is good for 24 months for promotion. Marines must qual every year and at a very high standard from distances up to 500 yards on iron sights. Being proficient as possible with your weapon (Expert) should be more than just hoping whatever your score was 23 months ago is good enough for promotion. This is that difference in culture I am trying to explain to you.
The Army, in this very article, explained this away as a product of deployments. But, Marines deploy too. There are no "gaps" in marksmanship, because infantry skills throughout the Marine Corps is expressed as being as important as filing a record or programming a radio. But this issue isn't just about sitting on a rifle range. It's about routine training with crew served weapons in the field, away from primary MOS. It's about routine patrolling and security exercises when on field ops. It's about routine comms courses in and out of the field. It's about creating a culture that understands that "every Marine a rifleman" means that ever Marine could be in a patrol along side a Grunt tomorrow or within a security detachment; and no amount of filing or mechanical know how is going to save his life or the lives of those in the patrol around him.
And this would be the entire problem here. You don't understand the slogan because you see things only through the Army culture you experienced. Our branch prides resonates in all of us, but there comes a point where we have to separate our pride from the reality of things. "Every Marine a rifleman" is not supposed to mean that every Marine is an 0311. It means that at any given time, all Marines must be able to perform next to the 0311. If he can't, then he simply sucks at being a Marine. There is no "oh, he's just admin" when it comes to needing a QRF. He needs to know how to operate a crew served weapon. He needs to know how to conduct himself on patrol. He needs to know that silly little things like body armor and his rifle are the most important thing to him when deployed.
Let me ask you...why do you think that the Marine Corps, with its full support system mixed among the infantry units of one division, spear headed through central and populated Iraq, while the Army with its vast infantry was relegated to the west in the open desert?