The question of whether Jews, Christians, and Muslims worship the same God is both revealing and foolish*. Though it is true that each has their own interpretations and ways of worship their is no logical way around the basic theology each claims to follow. Each claims to be monotheistic therefore they must worship the same God. How can they believe otherwise without inadvertently admitting to a false belief. Accusing the other "monotheists" of following a false god is incoherent. There can be no other god, false or otherwise, or even a god-like being under monotheism since such a system of belief would require the one true god to be all-powerful.
Basically, if each
truly believes in monotheism then they must follow the same god. That
they question routinely comes up seem to indicate that many theists
aren't nearly as confident in their beliefs as they'd like to think.
*Jeffrey Weiss' CNN Belief blog post, "Do Christians, Muslims and Jews worship the same God?", is recent example of this recurring question.