I would suspect that only those who knew they were going to be offered or were actually in service until 55 would have transferred to the 05 scheme. Don't forget, service beyond 38 is not guaranteed and the old pension scheme at least gave you a pension from that point. The new pension scheme gives you next to nothing until you're 55. It would have been a fairly dull choice to 'hope' that I would get offered PA as nothing seems certain anymore.
What annoys me is the fact that a change in circumstances, or terms of service, is not accompanied with an option to change your pension. I may find myself serving with someone who is doing exactly the same as me, under the same terms but, for an input to a computer, will get more at the end of it. Seems a strange method for the retention of personnel.