ev2012:

There are all kinds of ways to properly support stone, especially with custom cabinets. Your KD is making recommendations for foolproof methods; there are always tradeoffs.

We attached heavy steel L shaped brackets to some of our cabinetry for overhangs. They are *very* sturdy brackets "could hang a tractor" in the words of our GC. One one spot, they were attached inside the cabinetry . . . on another, they were attached outside (and hidden by some furring strips under the bead board) . . . on a third location, we did build a little supporting wall to hold them . . . but I had plenty of leg room there.

Our fabricators also offered steel plates -- I didn't see them, but my impression was that they are thin plates that would go under the counter (notch out of the top of the cabinet), from some distance over the cabinet and then protruding under the overhang. This seems like an elegant solution.

You can also have your carpenter build the support wall "sideways" with the studs only half as deep, so you just lose 1.75ish" instead of 3.5" . . . We'd discussed doing this but I didn't bother since we had lots of leg room on the one overhang where it might have been used.

who sells these steel support brackets?

We purchased support brackets for our island from Centerline Brackets online. The company makes brackets for several different configurations and has very good illustrations on the site.

Here is a link that might be useful: Centerline Brackets