I read it as follows:
Anyone who is eligible to upgrade between 10/2/11 and 12/31/11 and does not use it, can use it all the way until 12/31/2012. Upgrading during this period starts the 20 month upgrade clock.
So say you upgrade 10/2. This starts the 20 month clock. If you upgrade 9/16 we are stuck in a 22 month clock instead. This difference is only really 1.5 months. And to your point, I'm pretty sure that we could call and bitch bitch bitch and get sprint to upgrade us 1.5 months early. Everytime I call sprint and start waiving the theory of me signing a new 2 year contract I feel as if im a human surrounded by hungry vampires.. but that im standing in the sunlight. Sprint will do anything to get me to step out of the sun to taste my juicy juicy 2 year contract signature.
In the end this really really really aggravates me. If I had hesitation about waiting for nexus prime before, now i really do. One phone every 20 months starting 9/11/2011. Better get teh right one or you'll be paying $600 for your phone upgrades in the future!