One of the recurring themes I notice when I survey non-Orthodox Jewish blogs is how upset Heterodox Jews generally are with Orthodox Jewry's refusal to recognize their versions of Judaism as legitimate expressions of the religion. One recent post (I forget where) even emphasized that Orthodox is itself a recent invention so it should have no pretensions to greater legitimacy than, say, Reform.
I think a big reason for this is the influence of surrounding society. No sector of Judaism is immune to this. In fact, I'd be willing to wager that almost all sectors of Judaism fall prey to this influence. On the Heterodox side assimilationist tendencies and a desire to be religious "correct" mean allowing surrounding society's value to set the values of what they call Judaism. On the Orthodox side there is an increasing tendency to set Judaism's values davka in opposition to prevailing secular ones even when some of those secular ones (honesty in business, for example) are quite commendable.
If that's the case, why doe Orthodoxy set itself apart from the other so-called streams of Judaism?
It seems that this is based on the response to secular society's influence as described above.
Consider that in North America we live in a Chrisian-majority society. Now, how would one define Chrisianity? Well to keep it simple, it's a religion composed of multiple groups all of whom sharing one belief in common, that God sent Yeshu haNotzri to save us from our sins and then died for us. Other than that, when one looks at the spectrum of groups within Chrisianity one sees really very little in common other than that.
The Heterodox understanding of what Judaism is has been influenced by this. When one looks at the various groups in Jewish society one might conclude that Judaism is also a religion composed of multiple groups all of whom sharing one belief in common, that God did not send Yeshu haNotzri to save us from our sins, etc. How else to describe Reform's rejection of Jews for Jesus when many adherents to the latter are far more ritually observant than the vast majority of the former? When one looks at Humanist Judaism in one corner and Satmar Judaism in the other, there is really nothing else that the two have in common Jewishly. Like Chrisianisty, this is a minimalist position.
In contrast to this, the Orthodox position rejects the idea that Judaism is a religion like Chrisianity. The Orthodox definition of Judaism demands a belief in God, acceptance of the divinity, antiquity and unity of the Torah and the revelation at Sinai. Any set of beliefs that is missing one of those points is not authentic Judaism. In contrast to the Heterodox position, this is a maximalist position.
This is perhaps why Open Orthodoxy, despite its continued claims of fealty to authentic tradition, has been perceived as crossing the red line into Heterodoxy. One of its major decisors openly admits he doesn't believe that any of the history of the Torah is true. Other leaders extol the desirability of halacha being altered to accept homosexual marriage even if they haven't found a way to do it yet. Even its greatest rabbinic proponent, an internationally renowned posek in his own right, revealed an unseemly secular influence when he recently proclaimed that it was time to ordain women as rabbis because he wanted to accomplish it before he retired.
Keeping the concept of the surrounding perspective is important for the Torah observant community as well. The rise of "Taliban Judaism" in Judaism with Burka Babes and segregated buses is linked to the appearance of, well, the Taliban on the world and religious scene as well as a reaction to the increased lewdness and promiscuity of secular society. But just as the Open Orthodox are wrong to try and redefine Judaism along the lines of secular liberalism, we in the Torah observant community should avoid limiting Judaism to those chumros which oppose society's mores simple because we want to oppose society. Torah is not a shield from arayos, it is a way of living that serves as an example to mankind and as a result it should lead, not follow even in opposition.