Attrition

At one end I keep hearing that all the IT companies have got lots of mid & senior level resources & it is already saturated enough. It is brimming that orgs are forced to create new mid & senior level positions so that they can be filled in by the getting-experienced employees.
But it seems there is a newer trend that there is going to be more attrition in that upper levels like 15%. When there are no positions in the market, how is it possible to have such an attrition. But inorder to retain these employees, I'm not sure if 15% salary hike would really make a difference, as per this article.