The logical loop is that Caine isn't holding Cobb responsible (or at least isn't punishing him) for the act of inception that lead to Mal's suicide?

(Just making sure I understand you correctly.)

Exactly. It seems like from the outset, Caine doesn't think Cobb's responsible, but then his big revelation (in front of Caine's "student") is that he performed inception on Mal, which eventually led to her suicide. And now that Caine most probably has this information, he happily brings Cobb to visit the children.

Not reading this thread yet but...
 

Must see this film. Although, a kid in our cast blew the movie for me by discussing vital parts of the plot at rehearsal. Grrr...
:D

It's not like it was Cobb's intent to perform inception, and certainly not to do so in a way that would lead to suicide. She was losing herself, he tried to bring her back the only way he could think of, and it unfortunately back fired. Caine holding him responsible would be like holding someone responsible because they set up an intervention for their alcoholic wife, only to have that wife commit suicide in rehab because she couldn't handle being sober.