Good observation, VIBEELEVEN. It does have alot to do with a number of factors. Cost, accuracy, ease of use, effectiveness, etc.. These must all be taken into consideration..
It must be reasonably priced for huge amounts to be produced without 'breaking the bank'.
Accuracy is a big one, ofcourse, because what good is a bullet if it won't go where you aim it? (i.e. .22's tend to 'drift' alot more with wind and generally do not travel as far.)
They must be fairly easy to use with low recoil and fairly compact demensions so you don't haveto pack around gigantic magazines and mongo boxes of ammo.
And they must be effective, but do not need to be an overkill(no pun intended)...there is no need to shoot people with .3030's and make excessive damage if a .223 will disable them just as well without mangling them. The object is not to leave their guts on the ground beside them. Just to injure them so they're not a threat, and if it means hitting them with multiple rounds and killing them, so be it.
Does this answer your question?

 

Yes it does, very clearly and well put.

 

Hmm..If you would go back and read my first post in here, brucelee, I stated that I would shoot a trespasser with a Gloc first. That would be the closest gun at hand(how's under the bed?) and the most logical gun to shoot with. The AR-15 was put in their simply for kicks. But, if the AR was the closest gun to me at the time, I would not hesitate to use it.
As for the shotgun, I am a good shot, and that is why I would choose the buckshot over the birdshot simply because it takes more accuracy (and does not spray all over the place since I may or may not be at a distance of more than 7 yards).

 

Again, it's a GLOCK, not Gloc.

 

Lol!! Sorry I didn't catch that either time I posted it! Need to hone my typing skills..along with my numchuck skills and crossbow skills..

 

http://www.thegunzone.com/hague.html