Midarm machines start with about a 13" throat. Longarms start with about a 17" throat and can go up to 28" or so (maybe 32"?).
The Juki with a 9" throat is still a shortarm machine. The throat is bigger than most domestic machines, but still relatively small -- especially for frame work. This Juki is usually used for piecing and quilting, similar to quilting on any other domestic machine, but the throat area makes working on a large quilt easier.
Actually Juki recently came out with a longarm machine, and I thought this was the one you were referring to. From what I have read it's a nice machine but has some quirks and limitations that would rule it out as a choice for me. My "dream" longarm machine is an Innova!