[Timothee]

"Why do you think Apple has both a "Photo Album" and "Camera" app? And both a "Phone" and "Contacts" app?"

I'd say that in any case, they had to have Contacts and Photo Album apps for the iPod Touch and iPad.

Why also include them on the iPhone? Well, Photo Album has more features than the Camera app (access to Events, Faces…) so it might be simpler to have one codebase for a Photo Album app shared with iPod Touch and iPad, rather than trying to put all the features of Photo Album in the Camera app. For me, it's better too because it makes the Camera app more easily replaceable. (as seen with the OP)

For the Contacts app, I'm not entirely sure since it seems to be a clear subset of the Phone app.