A landscape is only as good as it is maintained. Maintenance is a big part of bringing a vision for a property to fruition. A variety of plant material is great as long it is maintained in an esthetic manner that compliments its function in the overall design of a landscape. Properly maintained plant material will adapt to its new micro-climates with the right plant selection.
A well designed landscape maintains well. Notice that turf areas are mostly in relatively flat spaces. They do not have a whole bunch of obstacles to mow around, thus creating a clean well maintained appearance.