"What is interesting however is the fact that political and other satirical type cartoons can be published in Britain, no matter how hurtful they maybe to the persons aimed at, but would any British magazine dare publish anything that may offend Islam."
I think usually it's because they don't want their office to be attacked or to have any of their staff threatened. The reaction from those they usually satire is covered in the Onion article (you can skip down to the relevant bit if you like):
"WASHINGTON—Following the publication of the image above, in which the most cherished figures from multiple religious faiths were depicted engaging in a lascivious sex act of considerable depravity, no one was murdered, beaten, or had their lives threatened, sources reported Thursday. The image of the Hebrew prophet Moses high-fiving Jesus Christ as both are having their erect penises vigorously masturbated by Ganesha, all while the Hindu deity anally penetrates Buddha with his fist, reportedly went online at 6:45 p.m. EDT, after which not a single bomb threat was made against the organization responsible, nor did the person who created the cartoon go home fearing for his life in any way."
IMPORTANT BIT: "Though some members of the Jewish, Christian, Hindu, and Buddhist faiths were reportedly offended by the image, sources confirmed that upon seeing it, they simply shook their heads, rolled their eyes, and continued on with their day."
I think most editors have to weigh up the real human threat to their staff and business - and most err on the side of caution.