There is a difference between blasphemy and the worship of false prophets. Islam fobids images of Muhammad, lest the images themselves become icons, taking away from the real person or idea. The religion supports iconoclasm by definition. A cartoon is designed to be just that, an iconoclastic image, so it is hardly likely to encourage worship of false prophets.
The cartoon issue is blasphemy enhanced by a general taboo of figurative images. A similar kind of taboo, for example, would mean that if you were brought up in a ‘Judeo-Christian’ environment the idea of a manual depicting someone like Moses or Jesus performing various sex acts, which would be acceptable in less prudish Asian religions, would shock you. In fact it may even make reading the above statement slightly irritate you. I suspect that the irritation that is felt by people who inherit the Muslim meme is the same but much larger.
The equivalent situation to the outrage over the prophet cartoons in a secular society would be if it were considered a similar affront to be messing around with an image that represents a country i.e. flag burning – and in many countries that is illegal.
Image:Jyllands-Posten Muhammad drawings.jpg – Wikipedia, the free encyclopedia