Need Clarity on Merged Dimension & Extend merge dimension

Hi,

After going through lot of videos & articles on merged dimension, I still find this concept bit vague.

Hence I tried replicating the below scenario explained in the http://scn.sap.com/docs/DOC-49941 article,

And i still dont understand few things,

Data Set:

My Output:

Please clarify me on the below based on the data set & my output,

1. I'm unable to include Salary into the table by having Emp_Id (from revenue) & Revenue, It says "Cannot drop here - Incompatible Object". Why ?
2. When i use Salary & Revenue with Merged Id OR with detail created for Salary & detail created for revenue with Merged Id, I get the same output as above. Why the Merged Id value is showing in all the columns ?
3. The behavior of Point 2 is the same when Extend merge dimension is checked/unchecked
4. I'm unable to replicate the below walk-through, What am i missing ?