Changing from the Chromatic to the Diatonic in the Middle of a Song - Part 1

Our most famous version of this is in the instrumental by George "Harmonica" Smith titled "Blues for Reverend King." In this he starts on the chromatic and then switches to the diatonic (C Chromatic in 3rd to the G Diatonic in 2nd Position). Listen to this track, along with my instrumental influenced by George titled "Dark Night" that I just posted on the BluesHarmonica.com Facebook page (http://www.facebook.com/bluesharmonica). We're not just switching to the diatonic and playing... what are we focusing on?

West Coast Down Home Harmonica - 60's Harmonica
http://www.bluebeatmusic.com/product_info.php?products_id=13475

"Dark Night" (D, C Chro in 3rd & G Dia in 2nd) with B.B. & The Blues Shacks last November at the Harmonica Masters Workshop in Trossingen, Germany.
http://www.youtube.com/watch?v=f6rl5fEIQek