Exactly.
Some people think that if iPhone 6 fits perfectly in their jeans - it should fit the same into any other person jeans... I can say, that these few centimetres make the huge difference when you are walking a lot e.g. here in New Zealand.

The thickness does not matter so much in this case.
As we have such a steep slopes all over the walking in my area - that the phone bigger than 5 or 5s just hurts the leg by every step when you are climbing. I like to walk to the work and back - it is about 5 km back and forth by such a slopes... So, the 5 - is no problem at all, I sometimes even check if it is still in the pocket.

But any bigger - it really
hurts, and I really can damage it bending the leg so much on every step...
There is no way to convince me that "it will fit perfectly" - as I tried to convince myself already with no luck.

As I really like how the 6 looks and its specs... I tried to fit it into my pockets, I played a long time with it, trying to reach the screen by one hand and trying to "not feel it in the pocket the same way as I don't feel the 5"... And I had no luck to convince me - it is
really not comfortable at all in comparison with my 5 and 5s
for my usecase...
Understand me right please: I do
not try to convince the happy owners of 6 or 6+ that their phones are to big, I just want my little 4" part of happiness too...