At a stroke, this move would help the procurement and long term budgets. It would also help the manning crisis, particularly across the Eng, GD(P) and NCA problem areas (particularly as many at ISK are eying up NetJets anyway).
It would also help BAE who have effectively squeezed as much as they can out of the project and now should be delivering.
The only people it doesn't help is those requiring the services of a Nimrod, particularly those on the front line- but since did MOD/Nu Labour care about them?
Not an expert (by a long chalk) but could this be linked to recent developments with the King Air?