Yeah, I have been sending cages in since the Breathe Cage II. They've made the same mistake before and I got a second voucher to make up the difference instead of another pair of Cages like you did. I spoke multiple times with Nike this time around, and they held strong to the statement that they've changed their policy. In fact, I just received another voucher--I stocked up on Cages at the outlet a couple months ago and just sent another two pairs in--for what I paid for them. I called and inquired again just to receive the same response. I requested to forfeit the voucher in exchange for a replacement pair of cages, but they refused. It wasn't an "our hands are tied" kind of comment but a "we won't."
At this rate, I'll get one pair of replacement shoes for every 3rd pair I send in. As soon as I've burnt through my last pair, I'm switching to another brand, probably ASICS, unless Nike starts replacing their durability guaranteed shoes with another pair. I go through them too fast to pay full/near retail, even though they are comfortable and fit my feet well.