They certainly are.
The site sales people want us to pay 50% of the extras, even though we've said our buyer is having a survey done on our house and we won't commit to anything until that has come back and the buyer is happy.
They must get really good deals on 'extras' on a new build, either that or the 'extras' are charged to you at 200% cost to begin with, to give you the impression you are getting a bargain when they 'discount' them! ... see also 'black friday' 'deals'.