One of the amusing, but also rather sad things about Debian developers is that they tend to have trouble with the difference between laws of men and laws of nature. So they write something down, and then they imagine that this has made it so.
We see this illustrated in the topic article and reinforced here.
Outsider: You have a secret members only list we don't get to see
DD: No, we made a rule which declassifies things
Outsider: Some of your members use pseudonyms.
DD: No, we made a rule saying they mustn't
And anyway the rule says no such thing, what salimma has written isn't the rule, and the most generous interpretation would be that they've "simplified" it for us and it just happened that this simplification removed all the loopholes in the actual rule. Becoming a pseudonymous Debian Developer is a bit trickier than getting pseudonymous contributions into Linux, but it's far from "simply not possible".