Devkits aren't exactly the same hardware. They have more CPU and RAM, and they run the development software to write code, export it to hard drive and recordable media. They weren't simply sold, they were licensed, and were supposed to be returned to Sony when no longer in use.

Units that say TEST are the part of the devkit used to run the created software for bug testing. Units that say TOOL run the Linux environment with the programming tools and compilers to make software for the platform. Sony only made TOOL units in limited quantities for licensed software developers for the platform, and more TEST units for them to use for internal testing.