I'm sorry I didn't realize someone had asked me about something or I'd have answered sooner. :oops:
Mitch's mom is right - you can do free-motion quilting on a LOT of different machines including those with drop-in bobbins. My first pieced quilts were quilted on a 401 and I often do darning-type repairs on my slants.
It's just that the vertical bobbin is more forgiving, as she says - fewer skipped stitches, no "eyelashes," etc. :)