There are a few things going on here:

1. The subject's hand may be considerably closer to the photographer, but not so much to the camera's sensor plane. The image was shot from just above the subject's eye level (looks like about mid-forehead to me), so the camera was tilted down.
2. You can only see the front half of what you're looking at, assuming it's a 3-dimensional shape with just about as much in front of as behind the widest point. But like the old Hollywood wild west town, it only has to look good from the front.
3. Depth of field calculations assume a given image size and distance, and while this photograph may look tack-sharp front to back when displayed on screen at this resolution, that tells you very little about what an 8x10 or 8x12 inch print will look like when seen up close and personal. (That's the print size that most DoF calculators are based on; they are overkill for web resolution and not nearly strict enough for larger gallery prints.)

As mattdm pointed out in his comment, there is no good reason (usually) to shoot wide-open in studio in any case. You may want to restrict depth of field for effect, but f/2.8 at 80 or 100mm is pretty meh for that at typical portrait distances; you've really got to go wider than f/2 to make the effect look like it was deliberate (and if you're using strobes, you may not be able to get down to the power you need without an ND filter, depending on the brand and model). Ordinarily, you would be shooting at something more like f/5.6 or f/8 to coax the maximum amount of goodness out of your lens (and to make up for any slight movement of the subject or the camera between focus and shooting — a couple of mm is all it takes to go from tack sharp to slightly mushy when you're shooting at very wide apertures, even when it's not bad enough to say you missed focus).