From Rockford Lhotka's Expert C# 2008 and VB 2008 Business Objects books
I did some more research, and now I have better understanding.
It looks like .rdlc are client side reports, and much easier to work with. I was actually referring to .rdl Server Based SSRS Reports, which I think it is the proper way to go. During my experience, client-side have always been problematic. So, I will not spend time on it.
With .rdl, it looks like if you want to implement a middle tier using a BO to retrieve your data, which is the professional way of doing the work (to avoid rewriting and redoing the work, and to utilize the work you have done before) in order to do that, you have to pay some dues, ie, you have to implement some minimum number of Interfaces of the SSRS Data Extensions.
Well, I need to spend some time in that. I will do some effort, and try to post back the results.
Tarek.