Thanks Joakim. Let me try to elaborate in answer to your question:
Holes 1-4 blow give you the tonic chord C major in 1st position, C E G C on a harmonica in the key of C. Holes 2-5 draw give you the dominant 7th chord G7 (if you add hole 6 draw you get G7/9). As my diagram shows, the available notes in other hole sequences simply offer different inversions or voicings of these chords, as the notes are the same but you start at a different point in the sequence. So 1-4 draw still gives you a G major chord, but starting on the fifth D: D G B D. In musical terminology, this is called the 2nd inversion.
Basically all regular tuned diatonic harmonicas offer the same simple and satisfying chordal relationships, whatever key they may be tuned to.
Hope that helps
SB