The idea that you can get the majority of 30 .22 magnum rounds into a target assumes 1) that you'll have TIME to fire that many shots, and 2) that you're that good a shooter, against a moving target.
In most domestic self-defense confrontations, it's generally quick, up close, and with just a few rounds being shot. (Often from little more than a few feet away.)
If you're a good-enough shooter to get a bunch of .22 magnum rounds on target quickly, I think you'd be far better off putting fewer, bigger rounds into an attacker, more quickly. The idea is to minimize the risk and end the transaction -- and while .22 magnum rounds aren't to be sneered at, they just don't have the ability to disable or damage an opponent as well as a larger caliber.
That doesn't mean I don't want one of those new Kel-Tecs, though. <grin>