Yeah. When Bonham died, that was basically it. Very hard to replace such an incredibly talented drummer like him. It is the same really with a lot of bands that split up; they're solo work never seems to reach the same heights. The Beatles is a good example of this. Although, Harrison made a good album, and Lennon did some decent stuff, it was never really as good as the stuff they did together. I suppose it is the sum of all those parts.
And speaking of Bonham, I love is work he did in this song.
http://www.youtube.com/watch?v=RgAFoyIgskY
The Bonham shuffle. Not really a typical Zeppelin song really.