still wondering why Conroy didn't do Under the Red Hood too, but that's neither here or there.
The general policy for the DC Universe movies is to have a different cast and continuity for each one. Andrea Romano talked Warner Bros. into letting her use Conroy, Daly, and Brown for Superman/Batman: Public Enemies as a special case. But then they decided to do a sequel, so naturally they kept the same cast, but it's the exception to the rule.
I assumed it was a TVization of the comicbook "All-Star Superman"...
Yes, that's exactly what it is -- although it's a direct-to-DVD movie, not a TV production.