This is what I think happens :
In the first few weeks very few people vote. I have a sneaking suspicion we would all be gobsmacked as to how few votes there are in the early weeks. So, odd decisions happen not based on dancing and the sad, GBP underdog vote has power.
Then, as the weeks go on and the competition gets serious, those voting increase but they tend to be the sort of person that votes for dancing. Add to this increase the fact that every time a good dancer goes - like Penny - her fans will probably pick a new favourite and that is likely to be based on dancing too. The underdog effect disappears unless they are truly popular people (like Julian was).
So, as time goes on, the truly good dancers and truly popular live to see the next day and those only gaining votes due to being underdogs do leave. The judges vote helps this even more of course. It can't stop some decisions (like Gabby v Penny) but it can stop others (like Kate v John).
I'm sure next week the judges will have Kenny bottom and then two dancers above on equal scores. That gives Kenny even more ground work to do to to avoid the bottom two.
We would have had a very different competition this year if it had not been for the judges vote. I reckon John and Penny would have gone much earlier and, in fact, Letitia could well have left early as well. We could well still have Stephanie and Gabby in!