Dan, your post makes an interesting point. Interesting inasmuch as none of the parties, including government officials all the way up the line, disagree that the search was illegal. What many people don't realize is that even where there is agreement that a search was not legal, the evidence obtained from that search is not necessarily inadmissible. Exclusion is one remedy, but there are others. For example a police agency can be sued civilly for an illegal search.
The exclusionary rule is not constitutionally mandated - it is legislatively created. So the issue in Herring is what the remedy should be where a search was conducted in good faith but was still illegal. The only reason our courts recognize the exclusion of evidence as a remedy for a bad search is to deter improper behavior, so the question in Herring is whether exclusion as a sanction would deter poor clerical work. I don't think there is an easy answer to that.