Has the car got surround cameras? If so, a replacement screen will cost in the region of £1k as it needs the cameras realigned afterwards. If that's the case, I can understand the dealer not wanting to cough up. Maybe do an insurance claim if the chips are MT failures?
Interesting thread; of all the comments, this one stood out the most for me and having read it several times, the suggestion to 'do an insurance claim' raises more than just an eyebrow: the 'damage' to the windscreen would have occurred before policy inception. It's deception. You can't insure a car and then expect the underwriter to cough up for something - preexisting - you found on the car.
When you buy a three year-old car you have to accept there will be some signs of wear. Some used car sellers may even have them 'detailed' out so that they're not immediately apparent to any prospective buyer. If you want a car to be perfect - virginal - perhaps a new one off the assembly line is the one to go for, but it won't be long before even that car will pick up chips and dings from everyday use.