Some modern houses do have crown molding while some modern houses do not.
If you have a custom house built and request crown molding in the house as a design feature then they will install crown molding.
If you do not request crown molding then they may not install it.
I love crown molding in a house and it makes the house look much better than a house without the crown molding.
When installed right the crown molding gives the house a more inviting look and adds value to the house.
When I bought my house I wanted a house with crown molding as it made the house look really nice although I would have bought a house without crown molding and had it installed later.
But already having the crown molding installed in the house made me want to purchase the house much sooner.