Excellent questions and observations Ahah,
Addressing them the best I can on this medium, it seems that the Abrahamic, Judeo/Christian/Muslim dualistic religions pretty much evolved isolated from the monistic contemplative religions of the east, Buddhism, Hinduism, etc. Not until the agressive expansion of Islam into India and other areas did the two streams of religions really "collide". True, some Christian missionaries penetrated these areas, but it was really Islam that spread out into Africa and the sub continent of Asia. The real Christian attempt to reach the ends of the earth was on the backs of colonialism from western European nations looking for materialist conquest and of course with the blessing of the Church providing conquest was for the glory of Christ. And this, not until well after the glory days of eight to tenth century Islamic expansion.
So the two types of religions really evolved in relative isolation. Recall that the apostle Paul indicated during his ministry that the gospel had allready been taken to the "whole world". It has not been until the 19th century that it would even be possible for the vast majority of Buddists, and other monists to be confronted with the claims of the Christian/Muslim/Baha'i messages.
Getting to the point, for a Jew to become a true believing Muslim, he would have to accept the teachings of the Koran which specifically endorse Jesus as a prophet of God. So within the "religious world" of the west, for one to be a "true follower" one would have to accept the line of succession from one prophet to the next to be truely respectful of the divine plan as adumbrated by the most recent chronologically.
It becomes a much more challanging concept to insist that a Hindu needs to acknowledge the western linage of Gods Messengers. Especially after how much carnage and havoc the maurading Muslims wrecked on them. (Of course they learned it from the Crusaders a few centuries before in Palistine)
To conclude, it seems that we are challanged to understand that each of these traditions originated with an individual who claimed to be a messenger of God, (even Buddha said there is no god we can comprehend, but endorsed the idea of a crator) and their influence was positive for a certain period until division and disunity for many reasons began to neutralize its force.
Obviously there is a pattern of renewal and "return" which should become apparent. Everyone of these spiritual giants talked of His "return" and gave evidence in their sacred scriptures as to the time, place or conditions which would be in place when that event took place.
I digress. Hope I have made some sense. Gotta go do a honey-do project. Back in a while.
carmel