The answer (to the title question) is no, due to a slight mixup in terminology. What Moxie says is (emphasis added)

>if you have to perform any cryptographic operation before verifying the **MAC** on a message you’ve received, it will somehow inevitably lead to doom.

Notice that he says MAC and not signature. The PGP group has [discussed this too][1], so you are not alone in your concern.

In other words, mac-then-encrypt is not the same thing as sign-then-encrypt. Sign-then-encrypt is preferred to encrypt-then-sign. For more discussion on sign-then-encrypt see [this question and answers][2].


  [1]: http://www.imc.org/ietf-openpgp/mail-archive/msg05526.html
  [2]: http://crypto.stackexchange.com/questions/5458/should-we-sign-then-encrypt-or-encrypt-then-sign