I think you are being far too kind in saying you can't imagine this was intentionally hidden.
Remember there was a calculator on the website which had you put in a fare/route and you were told the cost. That calculator clearly used the .029/.0256 ratio that is described in the wiki above, and did not contemplate any kind of peak/premium pricing.
In my mind there are two possibilities, either the peak pricing was intentionally hidden all along, or someone (a new hire from Delta no doubt) decided to implement this enhancement more recently and did not think it needed to be communicated (i.e. no one would notice?!). That seems pretty intentional to me.
I think the possibility that so much effort was put into communicating the changes, drafting detailed new program rules and FAQ's and creating a award calculator engine, but all the people who worked on that were just incompetent and forgot to include the peak premium piece is absurd - and an insult to incompetents everywhere.