Since the sites like Technoratti look or show tags and Wordpress also allows to add tags ..why is that functionality not available in the inbuilt blog feature on Ning. ??
No particular reason. For now you can either add them manually in the html of your blogpost following the rel-tag microformat, or implement this feature yourself if you have a copy of the code.
Would urge that Ning allows us to tag everything that's postable - I'm trying to set up a fan site which uses a variety of content streams, and I'd love the fans to devise their own 'folksonomy' for our archive.