Should referencing critical comments on papers that have been referenced be obligatory?
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.