This was well beyond an "undue burden" placed on the WPI and NIH/FDA studies. WHY NOT the CDC's piece of garbage study being reviewed again? Someone tell me why???
Here's a suggestion: Look at the calibre of the journals these papers a published in. While the journal rating is not necessarily an indicator of the quality of a given paper, it does reflect the amount of care the journal puts into making sure the papers are of a high quality. See
http://en.wikipedia.org/wiki/Impact_factor for some basic explanations and, just past midway down the page, the top ten science journals by several ranking systems.
Science is in the top ten of all of them, PNAS usually follows not too far behind. You don't see
Retrovirology there and you sure as heck don't see PLoS One there.
The CAA reports that using the ISI Impact Factor,
Science's rating is 29.78, PLoS ONE is not even rated,
BMJ ranks 12.827, and
Retrovirolgy ranks a sad little 4.6.
Science and
PNAS have a lot invested in producing the top quality papers. Reviewers are
actually reviewing the papers (as opposed to giving them a quick read), and suggesting improvements.
Speaking as a one-time reviewer of research papers for journals, asking for a few (hopefully simple) more experiments is not necessarily suggesting that the paper is inadequate. Sometimes a reviewer will
suggest a few more experiments, based on his/her professional experience, that would
strengthen[/ the paper. The authors can choose to do those experiments or not.
I don't know this all played out with Alter's PNAS. I'm just suggesting that it's quite plausible that reviewers, finding the paper perfectly sound, and knowing that it was being called into question, suggested a few simple experiments that would cement it's position. Alter et al may have been not only willing, but eager to spend a few weeks to slam and lock the door in the CDC's face.
It's also possible that the reviewers were unsure about the quality of the paper and asked for more tests. I don't think that's the more likely situation under the circumstances.
If the NIH/FDA paper was asked to perform additional experiements, would they have had time to do that already or in the time before the paper is now supposed to be published? Don't experiements usually take longer?
The following is my speculation based on experience, but I know nothing about the specific circumstances of the PNAS paper. Generally speaking, if a paper needs are serious rework of it's experimental results, that work could take months. If the authors are advised to do some clean-up or strengthening experiments, it would more likely take a few weeks. A reviewer suggesting something to strengthen, rather than verify, is not likely to suggest something that would be a huge undertaking.
Ordinarily this process would take place during the normal review process, the extra month of work would be fitted into the publication schedule and no one would raise an eyebrow. Apparently some of that happened with the Lombardi et al paper.
It's odd that this second review took place after the journal was in galleys, but given that the CDC questioned the paper, it's no big surprise to see PNAS, with it's reputation, ask for a relatively straight-forward further review, and for the reviewers to suggest experiments that would strengthen the paper. To us, this delay is scary; to PNAS it's just a brief delay and a shift of the paper to the next publication cycle. They're probably pissed at having to do the galleys again, though. 
The real oddity, in my opinion, is that the CDC should call the paper into question at this stage in the process.
I said when the delay was announce that we would see the Alter et al paper in August (the next publication cycle probably). I'm standing by that prediction (for the moment).
