If they are offering 2 years and we're only offering 1 then that might sway it for him, or if they are just offering more and it's closer to him for him (saves going through the Dartford Tunnel every day) that might also be a consideration.
At his age he has to think about his family and consider it might be his last pay packet - i'd have no hard feelings at all if he went.
That said, he didn't show any signs of slowing down last year though so I would imagine he could do it for another 2 years. For me there are parts of his game that are brilliant. I can't remember how many times he saved us last year. However he did make a few costly errors last year. Wigan away being one of the most high profile ones, but there were a couple of other ones in key games too. I see him maybe as a decent league 1 GK although I do have reservations as to whether he can take us any higher. But that's no slight against him at all. He is a decent player, and has been a great player for us. I would have been happy for him to sign on for another season but also not too distraught if we have to find somebody else. My son absolutely loves him and his song "England's number one". Although if he leaves, and is replaced by another Englishman, he will soon realise we sing it to every English goalkeeper we have.
It's always a gamble to replace your keeper, but JED clearly has decided what he feels Nelson is worth and as such, I would imagine he'd have somebody in mind to replace him for similar kind of money. You have to hope anyway.