I agree, pistols are better for this task than either rifles or shotguns because;
stray Pellets don't hit walls
decent amount of ammo (at least 10rnds, I couldn't use a 5rnd shotgun)
Accurate enough for precise shots
doubletaps are easier than in a rifle
manueverability is the best
reload time is fastest
one handed operation allows for the more favorable "light seperate from gun" mode
less "noise recoil" than a .223/6.8
.45ACP is a heck of a round
The only long gun I could use for HD is possibly a 10/22.
If I lived on more than 2 acres of land, then a shotgun or carbine would come under concideration for "out of doors" home defense. As is, my Para P18.9 (it holds so many rounds I think of it as a small pistol cal carbine in it's own right) easily hits 100yards 10" plates.