JTO,
I've said it before and I don't think it's changed. I think there is an unofficial and unwritten policy of encouraging people of all Branches / Trades to leave early. Having worked out that pensions are expensive and before people start to climb too high up the pay spine, get them to leave if their own accord.
Yes, it dilutes experience and increases your training burden, but it decreases other costs significantly, especially preserved vs immediate pensions. Plus, if people are leaving early, you can effectively introduce graduated training so the high end high cost training is reserved for those few they want to keep whilst the rest are trained to an adequate level to make up the numbers. We all know it's a short sighted route to go down, but it's accountants with an eye on the bottom line not operators that call the shots these days; they are the ones that hold both power and influence.