Everyone also discounts the other reason NIST (with NSA behind the scenes) might be shifty -- they know of a mathematical or computational exploit class that no one else does.

And therefore want to do things-which-seem-pointless-to-everyone-else to an algorithm to guard against it.

Without disclosing what "it" is.

Everyone's quick to jump to the "NSA is weakening algorithms" explanation, but there's both historical and practical precedent for the strengthening alternative.

After all, if the US government and military use a NIST-standardized algorithm too... how is using one with known flaws good for the NSA? They have a dual mission.