I have a lot of Vortex. They are OK... Kinda... Their expensive stuff is nice but by the time you spend that much there's better brands that don't market 's warranty first then the product like Vortex. My current complaint with Vortex is the Viper HS LR rifle scope I have. For an optic in the $600, which isn't really high end, I'd expect better glass. A warranty doesn't do any good if you can't even see through the scope because it is so light sensitive.
On the plus side...
I got a pair of original 10x42 Razors I've sent in. They rebuilt the binos and replaced the lense covers.
But as far as a rifle scope goes, all my guns will wear Leupold or Nightforce.
I don't know where you get the idea that Nikon loses value faster than vortex.The transferrable warranty might have something to do with it. It certainly adds to the resale value, and if you can sell your Vortex product for closer to what you paid for it, your probably more likely to sell it if you want to move up than someone with, say, Nikon optics, who will have to take a bigger hit on the resale price to do the same thing.
It seems that way looking at the classifieds, but I certainly haven't conducted a scientific study on the issue, but a transferrable warranty has to add value. I could be wrong though.
I actually own more Nikon than Vortex -- more Nikon than anything, actually, great stuff.