1. Being an equal opportunities offender, doesn't mean that the particular depictions of muslims weren't' racist. Vice, South Park, and Private Eye have all been good at lampooning all groups equally; that doesn't mean that they aren't often racist, homophobic, etc.
2. The point isn't that the cartoons are 'offensive', as Tanith mentioned above. I'm not saying that people should somehow be protected from being upset. That would be a fucking stupid and paternalistic argument to make.
3. Racism. Race isn't a thing. There are no 'races'. Oddly, if there were actually races, then that might well provide a justification for racism. Racialisation of a group is done through connecting certain (usually accentuated) physical features to particular cultural and social practices. Groups who have been racialized include africans, jews, serbs, arabs, chinese, japanese, asians. Race, then, can cut across cultural, linguistic, national, and continental boundaries boundaries; there is no meaningful taxonomy here, there is no stable and essential base for 'race'.
4. Race making is a process that occurs within society, and it is done through legal, political, academic, and (in the case of Charlie Hebdo) cultural practices. Groups in society are given essential characteristics, they are given a 'character'. Think about, for example, discussions and books on 'the negro mind, the jewish personality', the 'arab character'.
5. As I said before, race is constructed through connecting certain cultural markers with exaggerated physical features of the target group. The representations of Muslims in Charlie Hebdo do just that. The hooked nose, the scraggly beard, sunken eyes, and overall ratty depiction connected with so called traditional dress. Jews, were, of course, depicted in much the same way in 1930's Germany. Such a depiction is, historically, a one size fits all representation of both Jews and Arabs. As Said says, 'the transference of a popular anti-semitic animus from a Jewish to an Arab target was made smoothly, since the figure was essentially the same'.
6. As to the reason why this is important, there is, I believe a fundamental connection between cultural representation of particular groups and the manner in which said groups are treated, both by wider society and by the state. State racism always comes with certain cultural depictions of the particular group, to further categorise that group as a distinct 'other'. So, in 20th century America punitive laws against black people were coupled with particular depictions of black people in media: as ape-like, predatory, overly sexual, thick, servile. In the same way, state racism against muslims (see the article I posted above) is coupled with a particular cultural representation of muslims. Charlie Hebdo maintains and perpetuates this particular, negative, representation of muslims as a dangerous 'other'.
7. If anyone's interested, the key bit to read in Orientalism is the final section, Orientalism Now, where Said goes into the process of race making in the Orient (especially in relation to Jews and Arabs), and talks about its connection to, among other things, particular scientific and academic discourses.