I think the importance of simplicity is wrongly interpreted, even by the onces who achieve success through it.
The point they are neglecting is actually that the "concentrating" the design to the your important goals and contents is of utmost important and one way to achieve it is by simplicity. Its not the only way to achieve it. Hence, whenever people stress that simplicity should be the ultimate goal of design, I think its somewhat misleading.
The "concentration" to the important parts of design, prioritizing the contents before designing and placing your efforts to drawing the attention of users to these part should be of high priority. And of course many other important consideration follow in addition to this.