Six seasons seems like a real promise to the viewer, as well, "this is going to be worth your time, it'll end when it's ready to end and it'll stick around until it does."
The only other instance like this I can think of was FX buying a hundred episodes of "Anger Management" when it was still in the first season, but I'm sure that was motivated in part by sales, triple camera sitcoms sell into syndication much easier and Two And A Half Men is syndicated like crazy, so if you can sell a hundred eps of a Charlie Sheen comedy while the iron's hot, you're swimming it cash.
But there's no comparison in terms of content or quality, THIS is pretty exciting news.