I would say that a more advanced model is more difficult to operate, from the standpoint of a beginner. While they may offer features that enable faster, more reliable, or otherwise better performance in less-than-ideal shooting conditions, I would not normally recommend to a beginner anything above a Canon EOS 60D or Nikon D7000 as they are not worth the added complexity.
Past this point, you start to have more complicated control layouts and less assistance for the user to learn basic photography principles. These control layouts are designed to enable experienced photographers to quickly change settings and get the camera to work exactly the way they want, but beginners will only find that it gets in the way of learning the basic concepts. The Nikon D300S, for example, does not have a mode dial and requires the use of a MODE button and a separate control dial to select modes. There are no scene modes at this point, and it can become very difficult for a beginner to understand what the camera is doing and what he/she needs to do to get a desired result. The same holds for a Canon EOS-1 series camera.
Furthermore, a more advanced camera is larger and heavier. While they are often designed to be more durable as well as enable shooting in inclement weather, they make it more difficult to carry and can discourage going out with the camera. A beginner needs to be able to go out and shoot without having to deal with the weight of say, a 1.8 lb (820g) Canon EOS 7D - and this figure does not include a battery, memory card, or lens. These will easily push the weight towards 3 lb or more and will quickly discourage a beginner from going out with his/her camera. (The midrange Nikon D7000 weighs 780 grams, but with battery and memory card installed.)
On an entry-level or midrange model, all of the exposure modes are easily found on a mode dial and scene modes are easily accessed. There is often assistance on how to achieve a certain effect, and control layouts are simpler and easier to work with. While they may not offer the efficiency of more complex interfaces for experienced photographers, they allow a beginner to grasp the basic concepts of photography in a relatively painless manner. They are also lighter and easier to carry than a higher-end model as well.
For what it's worth, I use a Pentax K-r and I started out with the scene modes and tried to understand what the camera was doing until I got more experienced and learned to use the semi-automatic modes like Tv and Av. My camera is usually left on P to allow quick shots when they come up, but I'm perfectly happy switching to a more advanced mode. Had I started out with a K-5, I would have needed more time to learn the controls before I could do this, and since the K-5 does not have scene modes, it would have been more difficult for me to learn the basics.
To answer your question, a D7000 is fine, since it has scene modes and is still fairly beginner-friendly, but I certainly would not recommend that a beginner use a Nikon D300S, D700, Canon EOS 7D, 5D Mark II, or other semi-pro or pro-class camera, regardless of whether he/she could afford it.