I have long tended to own multiples of my carry handguns. Handguns are mechanical objects, which means they are occasionally down for maintenance and repair. As familiarity with one's carry gun is a good thing, and might make a difference between living and dying, this means a spare of the same model can be a good thing. Assuming one buys into this concept, one can then economize on holsters, spare magazines, and spare parts.
Owning two or more of the same weapon makes perfect sense to me. It makes little sense, to me, to own only one each of many different weapons; I am not much of a collector. (To be clear, it is quite OK to be a collector; it is just not my way.)
This concept is not just for firearms. I shoot evidentiary photography at work, as part of being a police officer. Digital SLR cameras are both electronic and mechanical; plenty of things can go wrong. My camera case contains two of the same model of Canon camera, though the lenses are different; one wide-angle zoom, and one fixed-focal-length macro. If either camera were to malfunction, I could keep working, by swapping the lenses as needed onto the one remaining
camera.
Presently, I own only one 1911. When I last used 1911 pistols for duty and carry, from 1997-2002, I "qual'ed" with three, the classic pair-and-a-spare. I subsequently kept a pair of G22 Glocks, and later three P229 SIG DAKs, for the same purposes. (I am presently down to just one SIG, in anticipation of a policy change that would let me switch to the gentler-recoiling 9mm as a duty cartridge; .40 is harsh to my aging, arthritic wrists.)