You all received written contracts from the warranty company through your dealer when you bought your sled, and every one of those contracts has a specific start date AND "term months" circled on it. Dig it out and read it (it says Polaristar at the top)...it's the only way for you to know for sure exactly what you have.
When I snowchecked my 08 Dragon, I chose the extended warranty and my written contract says it starts 09/28/07 and has a 48 month term circled. So that means my warranty expires September 28, 2011. And yes, one year later I got this same letter in the mail that you're asking about. I suspect all new Polaris buyers get them, and many of us who have contracts like mine that don't expire until 2011 can just throw the letters away and ignore them...and still be fully covered.