The reason this model is necessary is because, unlike the Galaxy S III sold on other carriers in the US, the Verizon version ships with a locked bootloader.
The price is not bad in our view because you will get 32GB of internal storage, which would typically cost you $649 if you were to get it from US carrier Verizon. According to the website, it seems that this model will only be sold in the Pebble Blue variant.
The Developer Edition will only be sold through Samsung's website and not through Verizon. No release date is available at the moment.