Should referencing critical comments on papers that have been referenced be obligatory? Say a paper submitted for publication in a journal by Prof. Bertie Wooster references a paper by Dr Augustus Fink-Nottle, but that paper was the subject of a critical peer-reviewed comment by Prof. Roderick Spode.  Should I insist as a reviewer that Prof. Spode's paper should also be referenced and the criticism at least mentioned, even if I personally do not agree with Prof. Spode's point of view?  

My intuition is that the reader of a paper should reasonably expect to be made aware of any element on which Prof. Woosters work is based that has been seriously called into question, so that he is able to form an opinion on the matter.  Am I being unreasonable in this expectation?
This depends on why you reference the paper. If you reference it because of the details that were later commented on, there is definitely reason to also mention the disagreement. I would consider that a basic aspect of any referencing of relevant literature. If, on the other hand the comments by Spode have later been shown to be wrong (Jeeves, 2008) or irrelevant the "historic" discussion has little relevance.

So I think your sense is correct. But, the necessity to reference both depends on the reason for referencing. The two are not eternally linked for every aspect of the original paper, only the parts where opinions differ and from which the discussion has arisen.