Cash cow? Releasing one unreleased live album of a 5 year old reunion show? Other than How The West Was Won and the Mothership compilation, it's not like they are that prolific, especially for a defunct band.
If it was up to Robert Plant I doubt he could give two hoot's whether it was released or not, but it's clearly something fans wanted. And it still took them 5 years to release it (and as you say, it's clearly not been touched up in the studio, as Jimmy's cock-up on Stairway and some of Plant's duff notes are all still there...)
It's not meant to be a perfect example of Led Zeppelin in their prime or a big come-back, it's just a document of something historic that happened once and probably will never happen again.
Like I say, i'm not really much of a Led Zep fan, but I found the DVD really enjoyable.
Niv