With the Pelican/Storm cases, is there a real difference between the foam and the padded dividers? Or is it more of a preference issue?
The dividers can be rearranged if (when!) your gear changes. The foam needs to be cut/plucked to fit specific gear. So, the custom fit of the foam will provide slightly better protection, for example if you were shipping the gear. But to 'rearrange' the foam, you usually have to buy a new insert.
For storage at home, the padded dividers are much more convenient. Personally, I have the dividers for all of the cases except the small im2075. For that one, the top and bottom of the padded dividers were too thick for the camera to fit. The thinner, softer top and bottom foam hold it tight. On the larger im2300 and Peli 1600, i use the dividers.
I don't actually use the dividers on the carryon im2500 - it's the perfect size to hold gear loaded inside my Lowepro Flipside 400 AW, for great protection on the flight (if forced to check) and the convenience of a backpack when I arrive. If taking only a small amount of gear, I load it in Toploaders/Lens Cases and put those in the hard case - again, for a convenient way to carry the gear when using it on the trip.