Indeed. That's why I'm interested in "tchuss". Here's my 5-second-haven't-had-any-coffee-yet theory: "tchuss" was a recent export from Italy north to Germany. The Teutonic tongue couldn't quite wrap itself around the more mellifluous "ciao" and instead substituted a surlier, more Deutsch sounding ending involving gnashing of teeth and snake-like hissing.

Erm...probably not, but unless the idea behind "bye!" in this form goes back to where Romance and Germanic languages became distinct from one another, I'd guess that it's a recent borrowing.