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It's not a Newton, it's a MessagePad. Newton is the name of the operating system, MessagePad is the name of the device that runs the Newton operating system.
Another device running the Newton OS is the eMate 300. It does have a home screen with a grid of icons. I have one right here.
The MessagePads also had icon grids to launch apps, but it defaulted to a notepad application when you turned it on. I have one right here.
I don't think it really matters what you see when you turn it on, Newton based devices and Palm devices all used icon grids to launch apps.
My Psion 3a uses a row of icons. If an app has user files they are listed under the app icon and can be opened directly from there.
It's not strange Apple went for this grid solution as it's easy to do, easy to use and the Macintosh in a way also had icon grids. Sure, you could move the icons and break the grid, but the basic idea was a screen with little icons that launch apps.