Adding webparts using an XML file

Hi
I have followed this link and it seems to work in the sense that it adds webparts from my XML file successfully.
http://www.carlosag.net/Articles/WebParts/catalogPartSample.aspx
However, the actual controls themselves are never displayed and their respective page loads are never called.
I am obviously not understanding something fairly fundamental here and would be grateful for any pointers please.
The controls themselves work fine if I hardcode them into the catalog zone and inherit them from user controls but when I change their inheritance to webpart and try and use the control from this example, as mentioned nothing appears. Clear as mud?
An example of a control - 
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