The bigger throat space really comes in handy, especially if you're doing large quilts, but bigger throat space is not limited to just machines that are called quilting machines. Some sewing machines have way more throat space than other sewing machines. This holds true for both newer and older model machines.
The IDT system on Pfaff is nice, and it's now available on other machines as well, quilting and regular sewing.
I've done nearly all my quilting on regular machines and, aside from the throat space, the quality of the stitching when quilting is about the same.
One exception was the quilts I did on a Pfaff Tiptronic. The IDT system was great and the precision of the stitches themselves were probably the best I've ever seen, the throat area was okay, they were small quilts for Project Linus so I didn't need a lot of space.