I received the following TPC review recently (a rejection):
The current version of the paper is incomplete, as important proofs (the novel results…) are left to supplementary material. This can be resolved, however would require a major structural change.
I think I would have preferred the TPC to simply say “we had too many papers, and yours wasn’t in the top X%,” rather then append this completely nonsensical reason for rejection. We put the proofs in the supplementary material because of space constraints. We could just as easily have omitted other things and put the proofs in the main body by doing some minor cutting and pasting. It may be a “major structural change,” but its also trivial. Perhaps they thought the paper was poorly written, but they did not say that.
Of course I’m disappointed that the paper wasn’t accepted, especially given that all the reviewers recommended acceptance. It’s clear that the real reason the TPC rejected us was that the scores were not high enough and they had to reject a lot of papers. It sucks to be on the bad side of a subjective decision, but it happens to everyone. Making up a pseudo-objective reason is about as useful as a little white lie. As it is, this description is about as principled as “your paper has too many authors,” or “your bibliography is too long” or “we cannot accept any more papers starting with the letter D.” There’s always the next deadline, anyway.