Some things not mentioned in this Watchtower article:
1) The Hilter letter quotes statements from Section 24 of the Nazi Platform as embodying "just principles" enunicated by the German government. One of these "just principles" quoted therein is a statement that the Party "opposes the Jewish materialist spirit (bekampft den judisch-materialistischen Geist) domestically and abroad". It was not necessary to quote this sentence to make the point that the Bible Students should have freedom of religion under the Nazi platform. Instead this expresses alignment between the Bible Students and the Nazi anti-Jewish policy. As a cover letter to the Declaration, the anti-Jewish statements in the Declaration (particularly with respect to accepting money from Jews, and the Jews owning New York) are thematically relevant to this quoted "just principle".
2) The Declaration distributed in Germany contains a statement that maligns American Jews and Catholics for "insulting the national government in Germany" and joining together to boycott the country because of the Nazi Party's "announced principle". This principle is the same one referenced in the Hitler letter, for the boycott sought to make Germany back down from its systematic harassment of Jewish businesses (which is in accord with the principle of fighting against the "Jewish materialist spirit"). The Declaration's alignment with the Nazis on the issue of the boycott in June 1933 follows Joseph Goebbels' announcement of a counter-boycott in April: "Tomorrow not a German man or woman shall enter a Jewish store. Jewish trade throughout Germany must remain paralyzed. We shall then call a three-day pause in order to give the world a chance to recant its anti-German agitation. If it has not been abandoned ... the boycott will be resumed Wednesday until German Jewry has been annihilated" (see http://en.wikipedia.org/wiki/Anti-Nazi_boycott_of_1933).
3) Although the article claims that the statement in the Declaration about "commercial Jews", in their words, "did not refer to the Jewish people in general, and it is regrettable if it has been misunderstood," the Society at the time did refer to the Jews collectively in general in such a manner. Rutherford wrote that "Judah and the land of Israel had commercial intercourse with Tyre, and doubtless from Tyre the Jews learned how to cheat their fellow man" (Vindication, 1932, p. 70), "the people now on earth and which are called Jews are a commercial people" (Favored People, 1934, p. 5), etc. There is thus probably no misunderstanding here.