After spending  ten-twenty  thousand dollars (or more)  to get the same convictions, would the Judge(s) in the cases of the ones who didn't actually cause the death impose any different sentence?

Most often, these plea agreements also include an agreement to not be able to appeal the conviction or sentence.

That saves even more tens of thousands of dollars.

And don't forget, Kitzhaber, and now Brown, refuse to follow Oregon law and actually use the death penalty, despite the votes of the people of Oregon.