They have a real friendship where they can say what they want to each other, insult each other and still laugh it off. There is nothing false about them and their chemistry is real. Its a genuine bromance, nothing fake about it and it is kind of nice.
It makes such a change from the false 'chemistry' we see with so many other presenters, where they pretend to find each other funny etc. and it just looks like they try too hard...yes Philip and Holly, I am talking about you.