While there is sincere belief and a good deal of lip service to shariah as the "unchanging holy law" of Islam, in fact it has historically been flexible and more open to change than conservative and literalist proponents assert. But among ordinary people there is a whole range of popular claims and fantasies about shariah. It often appears that it is as much about popular lore as law. Northern Nigeria is going through a period in which shariah is open to manipulation by populist politicians and they are using its populist appeal to the full among masses of people not educated in scholastic jurisprudence.
This is the same argument I have made before - that Islam is consistently applied as an excuse to justify socio-political self-aggrandizement. This is true of the subjugation of women, like the burka and bikini. The article is an in-depth analysis and well worth a read.
UPDATE: Matthew Yglesias comments with the example of 19th century imperialism.