Getting people right in any image is time consuming. Not only do we need to select the right sort of person, but we need a photo from the right angle and in the right lighting. It's time consuming. Many visualisation companies either don't put people in their images or make a really bad job of it and undermine the quality of their work.
We (and our clients) like to use people as they can help tell a story within a CGI. When done well, you can really add depth to an image and set up little situations that keep the viewer hooked for longer.
Since the early days of Blink Image, there have been 3D models of people that can be used instead of masked photographs. The 3D models can be placed within the 3D architectural model, so they react to the simulated lighting far better. Also, the perspective is spot-on because the same scene camera is being used to render them. The problem has always been that the quality of these models is 'so-so'. They tended to be used far into the background as they could tend to look a bit 'zombie' like!
However, things are slowly starting to improve. 3dsMax introduced Populate a while ago. Anima is another system that is quite clever. Other companies have also been slowly creating libraries of very high resolution scanned models of people that are getting better and better. They can still look a bit 'dead-behind-the-eyes', but we are getting there.
Many years ago, we had to use photography of trees and plants in our images as good 3D models just didn't exist. Nowadays 90% of the plants in our images are 3D. I think over the next two or three years we are going to see the same thing happening with people.