Well, if you read this site, you will often find the Christians are a remarkably heterogenous group. Sure, they all believe in Jesus, but beyond that there's some major differences. Some are attributable to different sects; Roman Catholicism, Happy Clappy, Amish etc., but some is just down to personal interpretation.
It's much the same with Muslims. Sure, all Muslims believe in the Koran and Mohammed, but beyond that they're no more homogenous than the Christians. Some believe it's vitally important to wear a full veil, some just a head scarf and some don't put any store by it at all.