Mike - I can't speak of the incident to which you refer, but I have been told by a serving officer with Hampshire Constabulary that regardless of what would be considered normal procedure in the aviation world, the Police have the power to breathalyse who they wish under the terms of the R&TS Act 2003 if they feel it is necessary to do so. It's possible they got information on the flight crew only.
As for why they didn't breathalyse the ground crew (or this was not reported) is anyone's guess, but they should have. I can't remember off the top of my head sitting here on a Saturday afternoon, whether the R&TS Act covers airside ground crew other than engineers, but it ought to cover any staff working airside.