More evidence that he doesn't have a clue what he's talking about:
I agree with your reader's assessment of Bosnian Muslim and Serb dynamics in your post. My mother suggested evidence from the Croatian point of view, as well. She's from Zagreb. She said the Hercegovinian Croats who moved to Zagreb were much more ambitious and "good at business" than the Croats from Croatia, and for that reason resented. But she said that the Muslims in Bosnia were considered to be even more ambitious and better at business than the Croats there--they were called "the Jews of Bosnia" (ironic, considering the generalized antipathy between Jews and Muslims today) for their business and financial prowess.
Memo to Steyn: some anti-Muslim bigotry is a lot like the old anti-Semitism. You need to be a little more careful who you're rooting for.