The services are cutting back personnel. They are scrutinizing personnel for promotion potential and performance. If they have not been promoted to a certain rank within X number of years, they are getting the boot (because in the military's eyes, if they are not promotable, then they are dead weight). This has been discussed within the military services news services (e.g. Army Times).
When the Iraq War was in full swing and we were getting bogged down within Iraq, the services, particularly the Army, lowered the standards for enlistment. They needed to make their monthly recruitment numbers. Now we are seeing those monthly recruitment numbers drop and with more cuts coming to the services, they need to re-evaluate their personnel strength.