A lot of people will post that they've used a iPhone for years and never got a mark on their screen. They must be more careful, lucky, or not have good eyes.
Without a screen protector most marks I get are not visible when the screen is on, but I still may get a small scratch that is always visible every few months or so.
I recently just started using a glass screen protector on my 5s that I bought from ebay for $4. It is great because you can't even tell it's there. I don't have to worry about my phone being in my pocket with my keys, lighter, other iPhone, etc.
I'm not sure what options are available for the 6. One advantage of getting the s series phones is that the accessories are a bit cheaper