User blog comment:LurkerLordB/Religion in a world without Christianity/@comment-3218619-20120424222609/@comment-1310192-20120424225715

...Sharing a single god with another religion is less of a base than having your whole dogma based on the other religion's holy book. Islam was based upon the Byzantine beliefs he learned on his travels through Syria.

If Islam was born in TTL, again, it'd be little more than yet another Semitic polytheist religion without any momentum and hence not an important god.