"(Slightly off topic, but I wonder why after 4 years and 2 tours in Iraq that this Marine is still only a Lance Corporal. Maybe promotion in infantry MOS's is slower?)"
I'm no expert, though I do have a son in the Marines who will be going back to Iraq in March. Most likely he has been perfecting his skill so that he hasn't had time to study for the corporal's exam. Or, perhaps he is one of those Marines who indulges in liquid fun and got into some trouble and has lost a stripe. Either of those a very plausible explanations.
(I have not served. My tagline honors my son and my cousin.)
Promotion is slower in the Corps than in other services, but he ought to have made Corporal by now- all other things being equal. Your speculation seems plausible.