That's what this public consultation is about every 4 years, listening to what the public have to say, and the feedback they have recieved this time around is that they have been getting a little too liberal with some of the ratings they have been awarding certain films in the lower categories. So that's why they are toughening up a little here.
Personally I think they should have kept things as they were, in fact if anything, got even more liberal with films classified PG to 15. But I knew this was likely to happen after the way they were criticised for passing films like The Dark Knight with a 12a (another media witchhunt last year directed at the BBFC). And also War of the Worlds and Casino Royale a few years earlier.
Anyway every years Mediawatch UK accuse the BBFC of being out of touch with the public by passing films like Antichrist uncut well of course the BBFC will say their guidelines are in direct response to the public.
We'll see how things pan out though, because you often hear the BBFC say things like they are going to classify more stringently and yet in the end there really isn't that much of a difference.
Fortunately the 18 will remain unchanged. Very little is cut for this rating these days.