It's like owning a car - just because you don't want to drive it as fast or as far as you used to, you still have to insure it, tax it and put petrol in.
Army recruiting is similar - training pipelines need to be maintained, promotion for those already in the system depends on a constant back-flow while natural wastage at the top sustains opportunity and hence retention. In addition, contingency levels need to be held and the system cannot just stop.
Perhaps not a particularly good analogy but it works for me.
Current advertising is probably aimed at 'sowing the seeds' 4 or 5 years ahead, so is focused toward early years secondary school students.
Current recruiting continues to replace the natural outflow of "time done" and early release individuals, some of whom will be casualties from Afghanistan.
It's always a balancing act between intake & outflow. With the ongoing financial situation nationally we have more applicants than jobs available at present, to the extent those we're training in the RN are finding there's a fair old wait to get to sea after completing trade training.
It will be interesting to see what the outcome of the defence review dictates...