Split-Coil Jazz Design - Downside?

[bowthing]

I am going to build some Jazz pickups, and the split-coil design looks like a good way to go. Since the impedance should be really close to a single coil, I am having a hard time figuring out why there would be any significant difference in sound. So the advantage of humbucking makes me ask the obvious question: Why doesn't everyone use them? What is the downside? Cost? Do they in fact sound a lot different?

The only things I can come up with by thinking about it is that the strings might be close enough that you can't get as much wire on them because the coil ends in the center would interfere with each other, and that the two inner strings might sound different since the adjacent fields are not both the same like in a single coil. Does anyone know if that is true?

Thanks for any help on this.