That's true for newer buildings that are purposely built to be luxury apartment buildings. But if you're living in a building that used to be an office building or a factory then it's not necessarily going to have a doorman. This applies to a lot of the old industrial buildings in SoHo, Chelsea, the meatpacking district, Union Square, etc. It's basically impossible to change where the elevator shaft of a building is after it's been built, because it's part of the structural support system of the building, so you can't just move everything around to add a lobby and front desk to the ground floor after the fact.