An article I was reading the other day reminded me how irritated I get when Haredim (ultra-Orthodox Jews) claim that their brand of Judaism is "authentic" Judaism, as it's been practiced for thousands of years; everyone else's brand of Judaism is thus "inauthentic."
One doesn't need to go back thousands of years to rebut such claims; a few hundred years will do. Here are some of the innovations the ultra-Orthodox have brought to Judaism since the 18th century:
(1) Cults of personality for rabbinical leaders, such that in some communities, the rabbis are not only spiritual leaders, but offer advice (or even demand adherence to their views on) various secular matters, such as whom to vote for, whom to marry, and so forth. A case in point: in a recent Ha'aretz article on a proposed boycott of El-Al by the Haredim, an international business man was quoted as stating that "my rabbi says this is my last flight on El-Al." For the unitiated, "rabbis," unlike say, priests, have no particular standing in Judaism as traditionally practiced; anything a rabbi can do, including marriages, bar mitzvahs, and what have you, can be done by any Jew. The idea of rabbi as holy man/guru is a recent innovation.
(2) Various additions to Jewish law that have no basis in traditional Jewish sources. For example, some Hardedim will only eat "glatt kosher" food; the normal laws of kashrut are not sufficient.
(3) Despite the traditional Jewish ban on superstition, superstitions are not only tolerated in many Haredi communities, they are positively a normative part of communal practice. Consider the practice of Kapporot--placing the burden of one's sins before the high holidays on a hapless chicken.
(4) Attire: where in traditional Jewish sources can one find a requirement to dress in the garb of 18th century Polish or Lithuanian nobility?
(5) Perhaps most dramatic, traditional Judaism always encouraged rabbinic scholars not to be a burden on their communities, and to have remunerative employment. Great rabbis of the Talmud are often referred to by their occupations--Rabbi so and so the blacksmith, Rabbi so and so the tailor, and so forth. Maimonidies, of course, was a physician. Today, in some Haredi communities, not only are the leading scholars of the community expected not to work, and instead study Talmud all day, the normative baseline is that all men, and especially younger men, should spend all their time studying Talmud, and working to support one's family is a last resort.
None of this is meant to disparage Haredi Judaism (though I have to say that I shake my head a bit when I see Haredim in B'nai B'rak wearing long black coats day after day in 90 degree heat), which has its own charms and appeals to its followers. But the idea that any of the above recent innovations they have made to Judaism would be recognizable to say, Maimonidies, much less Moses, defies credulity. The lesson is that even among the ultra-Orthodox, the religion has and continues to involve, and claims of "authenticity" based on total stasis makes powerful propaganda, but has little historical basis.