A'isha
Miss Schoolteacher
Sharia is derived from hadith which are effectively sayings of Muhammad, transcribed from Gabriel who was acting as God's secretary.
Actually, Sharia derives from two sources: the Qur'an, and the sunnah. Only the Qur'an is the word of Allah as transmitted to Muhammad through the angel Gabriel (supposedly, anyway).
The sunnah, on the other hand, is the words, actions, and practices of Muhammad and his Companions in their daily lives, which are recorded in orally-transmitted accounts called the hadith. These are not things directly spoken by Allah via Gabriel, but are the memories, recollections, and descriptions of what Muhammad and his Companions did and said as passed on by their contemporaries (again, supposedly).
Taking Christianity, another aspect is how the ideology evolves. Christianity has been allowed to move from the turgid goings on of the OT to lovely stuff like the Golden Rule through the coming of Jesus, but more importantly as a text the Bible is acknowledged to be the work of man and therefore fallible and open to interpretation.
This is not exactly true. See the concept of Biblical Inerrancy (and the related concept of Biblical Infallibility).
In contrast, the Koran is alleged to be the letter-perfect word of Allah and cannot be changed in any way. This makes a comprehensive theory of cherry-picking and mitigation very difficult, made more so by the agenda-heavy instructions of the Islamic scholars. Of course many Muslims do obey only selective parts of the Koran, and don't want to live under sharia, but in terms of academic Islam there is no justification for their stance.
This is also untrue. The text itself of the Qur'an (well, the consonantal skeleton known as the rasm, at least) is considered to be the letter-perfect word of Allah, but figuring out just what that rasm says and means has long been a topic of intense scholarly debate within Islam itself.
