The long road from literary interpretation of a concept to another media, such as television or film. When a novel goes from book form to movie form, for example, it can sometimes be a long road, rife with trouble. There is no guarantee what is there on the page will translate well to a different medium and sometimes changes must be made to fulfill the potential of the work. It must be done, however, because a book (or comic book) is not a movie and vice versa.
But of course by doing this, you risk alienating the core fans of the original work. But then again, if you stick too closely to the original work, you run the risk of not translating well to TV. The Walking Dead is no different in this respect. It seems everyone is happy for the most part in what they have done with regards to the show. It does not look like the comic book fans are all that rabid anyway, to be honest. It is not the same level as The Lord of the Rings, for example. Fans of that franchise are hardcore.
The Walking Dead have garnered fans mostly due to the TV show on AMC, a highly successful program about a fictional Zombie Apocalypse. It had a leg up, before it even became a show, thanks in large part to the involvement of Frank Daramont, the writer/director of The Shawshank Redemption. With he and Gale Anne Hurd of Alien, The Terminator and other big time film franchises fame, The Walking Dead was up and running hardcore.
After only 6 episodes, the second season was picked up almost instantly and the order was more than doubled to 13, than expanded to 16 for both the third and fourth seasons. Wham, bam, thank you ma’am! The Walking Dead was a success right out of the gate, in part to the already established fan base of the comics.
With AMC promoting the hell out of it and other companies jumping on board with other media, the show seems unstoppable. It has a foundation for success and with such talented people on board, there seems no chance of it running afoul of its fans, much like the vaulted Lord of the Rings trilogy. Peter Jackson crushed that and it appears they are taking a page from his playbook.