I disagree that the location of the camera is counter intuitive. When I am using my phone(using a wallet as an example here), I hold it in the palm of my hand - exposing the upper corner of where the camera is naturally. This is the way that I normally shoot images with my smartphone.
If I am typing, I use two hands, but the same corner is still exposed easily for taking a picture or video.
The reason that typical cameras have the lens located in the center of the unit is based on a few things. When modern film cameras were signeddesigned, obviously the film was being pulled out of a cartridge, across the exposure area, and into another compartment for post shot storage(sorry I don't know the technical names for these things). When digital cameras were first being produced, manufacturers could obviously alter the design since no film is involved, but as you can see the design is still very much similar to what film cameras were designed.
When you talk about cell phones, the primary function of the device is for talking on the phone, and using the screen to find information. Being a camera is a secondary function. Some smartphones are designed to be more usable as a camera, and as such they have some different configurations for the hardware. For the most part though, a standard smartphone will keep the primary functions in mind when considering design.
As others have pointed out already, the location of the camera lens does make a great deal of sense when you are using the screen as a viewfinder, or holding the smartphone one handed. To put the lens in the middle of the back of a smartphone, would have the user cover up the lens in most usage cases.