Actually a 4-5 pound trigger is about right for a duty-defense pistol, unless you're talking 'point-bang' poly-pistols, in which case you can add a half pound or so. More important than the actual pull weight, is that the final stage is crisp.
That last applies to target guns as well; but the low end of the weight scale is controlled by the design. I know about what you can get away with 1911's & revolvers...if I needed to know what was safely possible with the XD, I'd probably call Scott Springer.
On the issue of target guns in the home defense role- if you are under siege then you fight with what you can get your hands on, whether it's a hatpin or a howitzer. I keep a .357 DA revolver within reach of where I sleep, along with a nearby 12 gauge or rifle in the event I get time to roll out and fight standing up. Heck there's even a shaving-sharp 1903 Springfield bayonet handy, now that I think about it
