If they stopped making 870s tomorrow and you come back in 45-50+ years, you might start finding some parts a little hard to find, too.
I like the 870, they're really good guns, they work well, and they are "slicker working" with their twin action bars than the old model 12.
But I love my Model 12. Its the premium pre WWII pump design. Post WWII, 870 design rules, but then, they had decades of watching the model 12 (and others) perform in the field, on the streets, and in war, to improve on.