[happyfeet]

One gives constructive feedback only if they really care and do not mind spending some time explaining why you think there are flaws that need to be corrected.

Several of the managers in companies have the habit of saying "well done" to top performers with top rating during performance review & have nothing constructive to say. Does that mean they have nothing to improve in current position & they should just vacate the place so their direct report can take his/her place?

As Mark says in the article, it is the difficult path. To take a stance, have a point of view & explain why it is so. The easier option is to say "great work" & just run away. I am learning this more often in areas that are new to me - say in appreciating designs & colors that I am not so good at in web design & so on.