I'm not a big photography or video buff, but can't you download content from your devices via USB? [/quote ]
That method, even if can make device into a 'standard usb disk target", sucks much more battery life out of the camera. Plus you can't do it in parallel. For pros, as long as the camera is a disk drive pretty restricted in it being a camera. The alternative: swap to new card in camera can continue to shot while the other card copies over to the Mac. Who cares if it is going to take a couple of minutes because SD is "slow", you can do something else.
Similar factor for phones and MP3 players. If apple doesn't write a synch program and the vendor doesn't write one.... can often synch by just copying files. Yeah it is harder to do by hand but a manual solution is better than no solution.
So, why add the SD card slot to this model?
Probably because a boatload of users told them they had use for it.