I've heard that before, but my argument is that I'd rather have three small holes in a dead attacker than one big hole in the wall next to a live attacker. For your average "home defender", a .45 is too much to handle effectively. For one thing, the recoil on a .45 is just too exaggerated to recover from quickly. That gives you one BIG boom followed by a lingering lost second or so while the barrel is brought back under control to place the next shot (the one you won't get off because that lost second was just enough for the assailant to close the distance between himself and the now defensless, previously overly-well armed defender). I've got no argument with a .45 as a defense pistol, it will certainly get the job done in experianced hands. But it will only be effective if the owner spends the time to "get over" the shock of actually firing the thing and spends the time learning to manage that recoil, while the "barrel bounce" on a 9mm is much more forgiving and lends itself to a second or third pull on-target instead of the powerful first pull that careens slightly off-target because the shooter flinched while anticipating that big BOOM.
You're right about the over-penetration with the 9 though. Even a solid center-mass impact has a chance of paying your neighbor a visit after it exits through the "back door" of the uninvited guest. Sobering thought. That's why I tell my neighbors to sleep on the floor and stay away from their walls. Just because I care... :)