In my opinion, the Adventure paths are quite different from an standard campaign, including the GC. Not in content but in the way the material is published.
In the past the writers used to write huge campaigns in big books (>128 pages) full of content, mixing adventure information and background. Maybe it was the way edition business worked. Buty Paizo's business was about issuing full color magazines of around 100 pages monthly. So the concept they developed for the adventure path is to get several books that usually will be shorter than the campaigns aforementioned, consider a range of 64-100 pages with the adventure section clearly separated from the background, with really good design and illustrations and some supporting free background, usually a pdf with a player guide for the adventure path with the information that players can know.
Check here for more information: http://en.wikipedia.org/wiki/Adventure_Path